Check out this video by MMX. He goes step by step. I went plus .050 and rounded to the closest number. I bought my push rods from BTR and they had the length I needed in stock. I am using an early short block with eagle heads and stock thickness head gaskets on E85 and 8-10 psi. I used an old pair of push rods cut them and chucked them in a lathe and made my own push rod measuring tools. Not sure if any of this helps but I wanted to throw it out there.
