Exhaust exhaust manifold leak

Still sporting cast Iron manifolds but have used copper gasket ones in the past on other small blocks with good luck

I think I'm using the copper gaskets on my engine as well, but I have aluminum heads which all but eliminate any chance of imperfections on the head side. I also used a copper gasket at the collector. I have no problems with exhaust leaks from my set up anymore. The exhaust leak that I thought I had before I pulled my engine a couple years ago was due to not having set screws in the thermacitor holes on the back side of the heads. I must've forgot about them when I first built my engine in the early 2000s. You may not have the same problem, but it wouldn't hurt to check them out to make sure they're plugged or you may end up chasing your tail for a very long time - trust me on this!! lol

This is obviously an aluminum head (which just so happens to be a Trick Flow head and what is on my car ) , but do you see the larger tapped hole? That is where you'll want to make sure you have a plug of some sort.

You may not see the plugs, they should basically be set screws blocking the holes off. So if there are no set screw plugs in the top holes, you may need them. I'll try to remember to double check the E7 heads on my GT later as the engine is completely stock, but I'm 99.99% sure that the top hole is what needs them. I don't recall the size, but again I have Trick Flows on the engine in my II. 5/8" sounds right for that application anyway. They may not be that size on stock heads though, I'm not sure.

The valve spring wobble worries me.

I checked out my 87 a little while ago. As near as I can tell there is 3 holes like on the Trick Flows that I shared. It's pretty hard to tell with the engine in the car with all of the accessories still mounted though.

As for your valve springs wobbling, do they still have pressure on the valves, or are they a tad loose as well? You should be able to purchase shims to ensure your valves are preloaded as they should be. That's assuming your springs are still in good shape. There are a couple things that could be in play with this. First, I think you said your engine is a 69 302? It's possible that your heads don't have hardened seats which, over time, can affect your spring pressures. Then there's the age and fatigue of the springs. That could be as easy as ordering a new set of valve springs, which may not be a horrible idea if your engine is still running the original springs. Then you could set the spring preload to manufacturer's specifications and be good for many miles.

Here are answers to your questions:

1) Yes, it is possible to swap valve springs while the head is still on the engine. You will need adapters to connect compressed air to the spark plug hole of the cylinder you're working on. That allows the valve to stay in place when you remove/replace the spring.

2) Here is a good and fairly brief description concerning setting preload. All preload is is the spring installed height.

3) It is usually called out by the cam manufacturer. Assuming you're still running a stock cam, you should be able to just ask at your local parts store for valve springs for a 1969 Ford 302. If you have an aftermarket cam, you'll need to know the specifics for that cam - I.E. manufacturer, cam model, etc. Then you should be able to locate all of the information you'd need to purchase valve springs - open/closed pressures, installed height, etc.

4) You may need valve spring shims to adjust the installed height of the springs in order to meet manufacturer's specifications. Here is a link for Comp Cams shims, but there are probably as many manufacturers that supply shims as there are cam manufacturers - probably even more than that! Really all you need to search for is "valve spring shims" and a plethora of options come up on Summit's website.

I hope this all answers your questions!