Engine question

Well that is the whole point of discussing the piston=to head clearance. If the Felpro gasket ends up being .047" and the pistons are ALL .018" above deck, then you would have .031" clearance between pistons and heads. BUUT:

• You have an old engine, and with wear, then pistons may stick up higher and now you have reduced clearance.
• Not all rods are the correct length, and if 1 or more are long then that is also reduces piston to valve clearance

Clearances like .031" are OK IF everything is well set up and each dimension measured. MoparOfficial puts everything accurately to the proper dimensions. You don't have new parts and I'm going to guess that none of these things have been accurately measured. In that case, no way can I recommend that you use run anything like this tight piston-to-head clearance. IMHO, a KNOWN thicker had gasket in the .055" to .060" thick range is needed to put these heads on this old short block. Assuming it has the stock early 340 pistons.

What year 340 is this?

BTW, how well is this engine running now? Have you done a compression check on it? The reason to ask is that this is a pretty big cam, that is only gonna run at high RPM's......

Also, is the original torque converter in the car?