compression ratio

I have formed the habit of adding 2-3 cc's over the 'stock' numbers that you find, based on some actual measurements and a lot of reading on what others have found. You also need to learn about pistons and the amount of chamber volume contained in the valve reliefs or dishes. For new pistons, you can get that off of most manufacturer's websites. And then you need to know the piston to block deck height; the stock 318's are 'down in the hole' by around .080" as an estimate.

With those factors, along with head gasket compressed thickness and standard bore/stroke info that you can find anywhere, you can use a calculator to get a good idea of what you will have. (It may take some time to make sure you are putting the numbers in right; some take + or minus for the same factor.) I like this one:

http://cochise.uia.net/pkelley2/DynamicCR.html