I guess I wouldn't say pistons made 40-50 years ago are "available" I didn't even think about spending $600+ on custom made pistons, a huge error on my part. However I think I will stick with my original plan of milling the block deck and head surface to raise the compression.
I am still confused about "squaring the block" maybe it's just a different use in terminology. I would say align boring the mains is to make all the journals round, make them all the correct size, and make them all in alignment with each other. The deck surface is milled parallel to the crank centerline thus making the block "square" The cylinders are bored 90 degress to the crank centerline thus making them "square" That is what I would call "squaring the block" If the deck surface were at a "slope" then the deck should be milled at a slight angle (which would be parrallel to the crank centerline) making all the pistons at the same height.
Personally I would always align bore the mains if swapping main caps from another engine.
Thanx everyone for the specs on the mains and head gasket thickness. The shop manual I have for this engine doesn't list any specific specs but my 53 shop manual does and I didn't know if they were the same between 235s and 261s. I didn't mention it before but my block is a 59 so I don't have to worry about those main shims.
