Weight of the world... On 6 bolts?

People do it all the time....I would not trust it and would be afraid of damaging my intake, and then the motor when it falls. I bolted the chain to the front and back of the heads. It worked pretty well. Those bolts are bigger and the weight is not pulling straight down on the threads.

I lifted my engine with the four outermost bolts of the upper-to-lower intake.

So with that in mind, 6 MIGHT be enough to hold the engine and the trans.

But always better safe than sorry.

It's not that heavy (the engine and trans). we're talking what....700 lbs max? ONE 5/16" bolt will hold that just fine. I've seen & done a WHOLE lot more weight than that. Carb plate with 4 5/16" bolts holding up a complete 460 with a C6 and transfer case (front accessories and all). That's over 1000 lbs.

Years ago when I younger and dumber, and I worked at a salvage yard, it was not uncommon to wrap a piece of a seatbelt around the distributor base and pick it up. I had a coworker that was mechanically as sharp as a bowling ball, and at one time he had "forgotton" to cut the engine mounts on a 351M in a '77 F100. I started to lift it with a seatbelt and distributor and picked up the whole front of the truck. Dangled there for a good while before the seatbelt broke where it was wrapped around the fork and the sharp edge of the fork cut it. That was using ONE 5/16" bolt and a cheezy aluminum distributor to hold it. The distributor and the hold down bolt did not budge. Have also picked up 460's using nothing but the one 5/16" hold down bolt through a chain. Works fine (scrap metal recyling).

As long as the lifting plate is in good shape, it is fine. I'd be worried more about the plate and chain(s) than the bolts that hold it onto the intake.

The bolt thread has to be two times the dia. Going into alum. For the threads to hold. And the 5/16 x6 will be enough.