Best small block book

I agree, you should check the deck height of each piston in the engine. I noticed that #1 in my 340 engine is about .015-.020" lower than the other 7 pistons. This is probably a result of tolerance stack ups, etc. In my case it results in a cylinder with a slightly lower compression ratio, which hasn't been a problem (car runs 12.86 @ 105 in the 1/4).

In your case: if one piston is too tall then is a problem. Also, check whether cam is degreed properly, if it off a few degrees it might be the closest valve to piston distance occurs on cylinder #5.

Bob

PS: I use the MOPAR Performance A-engine as my guide to building my engine, since I had a stock short block with MP purple shaft cam and valve train. I have an old MOTOR manual to get torque and clearance specs.