340 input (direction)

Measure the combustion chamber volume. Then take other measurements I suggested. Those will help you to ballpark your compression ratio. With heads pulled.get a look at the.pistons and you can also remove the casting flash and junk in the intake and exhaust ports. Be careful though to not hit a water jacket.
Im doing this all myself right now as well. Amd.learning a lot. Im damn near 50 amd always worked on my own wheels. Im now starting to understand how the seperate pieces work together.
Just dont be in a rush. Enjoy! I am