Some say that the early 360 block walls were cast the same as a 340. The 340 was .040" larger bore to start with, and many will bore a 340 .060" over. If the walls are the same casting, then a 4.100" bore would be the same in either a .060" 340 or a .100" 360.
I would have one sonic tested before wasting your money, though. Even if it's true, core shift happens, and you could build an engine that is weak, ad likes to overheat.
And as far as finding pistons goes, when playing with a stoker crank, it's very easy.
