Engine 302 production block selection

The Rub:
Well, fellas, I've gotten a top end together that I will swap onto a stock or stockish block, probably this winter. My car's running great, and I'm not in a hurry. So, I figured I'd use the opportunity to try to find a budget-friendly upgrade. I know the mexican and older '60s era blocks had thicker main webbing. The old rotating assemblies up until '82'-83 were also 28oz instead of 50oz, which should be better for higher RPM.

I could refresh the stock block in Black Jack, but it'd be nicer if 1) I can swap complete motors in a couple days and have a running car again quickly, & 2) get a better shortblock at the same time.

So, that said, I would appreciate validation of my understanding and/or advice. I believe that pretty much any '60s era 302 block up through about '74 (exact year?) is considered an "early" 302 and has better quality iron & the thicker main webs than the later 70s & 80s blocks.

How to ID (quickly googled):
- In general:

1. mexican blocks:
a. “HECHO-EN MEXICO” stamp visible if block is disassembled
b. two iron knob-like protrusions just below each head on the front of the engine casting. The tips are circular and slightly larger than a half dollar. The left knob is not entirely circular, but usually has a flat bottom.
c. Came in late 60s, early 70s Rancheros and Torinos, vans and Trucks
2. 'Early' 302: Aside from the part numbers...?
3. Original Boss (yeah, right, but a man can dream): DOZE-6015-B stamped. 4-bolt mains.
4. 289 standard & "Hi-Po"...
5. Any others I should be considering?

Conversion Considerations:
In terms of converting them to work in place of an HO roller block, what adjustments are required?
- Early block head bolts are fully blind and don't need sealant on the head bolts
- Non-roller blocks require either link bar lifters or drilling and tapping the lifter valley to accept the stock spider and lifter tie-bars (M-6253-A50). Any adjustment to lifter bores or anything else I need to convert? Will it accept the same link bar lifters as a stock HO block? Diameter, height, etc...
- Aren't some of them 162 tooth flywheels instead of 157?
- I'm assuming they use the same engine mounts, and believe I've heard the stock bellhousing bolts right up. Correct?
-What else am I missing?

The smart buy:
What would you expect to pay, and whats the best way to minimize the chance of getting a bad motor? As a quick observation, there's a 302 from a '74 F100 listed near me for $450.

The ideal would be to get a chance to see the car running and then pulled after the purchase agreement. I think generally, I plan to stay away from anything that's been hot-rodded before me. So many folks are willing to lie about their 347 that's really a 302. I've read other stories from builders that said when someone mentions a problem, it is in their experience never the problem. It's always worse. Still is there any advice on basic checks/inspection one can do to help your chances of not being taken advantage of?

I've got some relevant old pics that likely came from a thread here or elsewhere...

First of all, when torn down to the lifter valley, mexican 302 blocks are very easy to identify:


When you can't get to the lifter valley, the easiest way to tell is the knobs on either side of the front of the block under the heads. On the driver's side it's right next to the oil pressure sender:


Lastly, the code stamped onto, I believe, the passenger side above the oil pan rail should be one of the following:
C8AM, D1ZM, C8AZ-B, or 75ZY-AA. I'm not sure if that list is exhaustive, but I can personally confirm the first one. The second apparently came in the early 70s mustang and is less common. I just found the last two through a bit of research.

Mexican:


Stock:


Mexican:


Stock:


Mexican:


Stock:


Mexican:


Stock:


Mexican:

limp said:

The few mexican blocks that I see pop up have been ridiculously priced....

Click to expand...

Yeah, I'm kinda thinkin' an 'early' block is most probable. But... People with A4s, R302s, and Boss's almost always know what they have. Mexican blocks can still slip through the cracks if you know how to spot 'em. So, good to know what to look for.

Honestly, I don't buy the 'nickel content' theory. I would hold them with the exact same category as the early blocks until I see evidence otherwise.

Yeah. The idea is to keep it cheap & easy replace short blocks. That will give me the peace of mind when I'm trying new things, and maybe to push a little harder on the sauce.

As to the RPM, I'd never rev an stock HO shortblock above 6,500. But the combo would probably optimally shift at or over 7k. I think I'd have problems with the T56 at that point. So, yeah. If the older blocks are good for 7k without internals, that might be nice.

I hear a lot more of that, these days. Seems somewhat random to me. I don't think folks ever insisted every shortblock would consistently go right at 500 rwhp. Rather, it was a measure of safety to stay shy of that & of 6.5k RPM. But not every, or even most would go at that number. Maybe it takes 7k RPM and 600 rwhp for years. Maybe not.

Seems like the major issue is main cap walk, caused by high RPM, high power or both. Then, torquing the main bolts starts a crack that extends upwards and eventually to the lifter valley. I've always had the philosophy of keeping the shortblock cheap (stock) so when it went, it didn't take an expensive rotating assembly with it. Then, ya just go get another one. But then, I don't want to push beyond 6.5k or beyond whatever a 150-shot puts me at, which should be between 450 & 500.

The only shortblock failure I've personally had was most certainly due to the tune/detonation under boost. That one bent a stock rod.

True, though I have 2 foxes with Dart Iron Eagles in them. This one's a little more budget-minded.

Mexican, early 302, Original Boss... ya know... whatever I can find.

Unless someone tells me otherwise, I think I've been wasting my time looking for an early or mexican block, based on the fact that they'd require a 'small base circle' cam. I already have a cam, meant for a standard roller block.

My understanding is that with my cam, the lifters would push upwards too far out of the bore. I thought all I needed was link bar lifters (or a dogbone installed).

Since I've never toyed with with idea of getting an older block until now, I've never realized this. Is that true, or can I still use a standard roller cam in them?

You know... I just got a conflicting signal in a truck forum that implied that there are 'retro-fit' link bar lifters. Would that be different than just a 'link bar lifter"? Are they shorter, or something, to ensure that they don't pop out too far? Or perhaps that forum was just off-base. If I can just use a standard roller cam, then it's still game-on in the parts hunt. But, if I can't, then I'm not going to look for the old style block anymore. I'm pretty set on using the cam I've already got.