360 block help thank you

Unless you yourself are a machinist, it will be cheaper to buy 360 pistons for what you want. In order to put 340 pistons in a 360, you will need to cut the top edge of the piston decks at a 45 degree angle, to I think .200 wide....IIRC? Then you need to mill the skirts to clear the counterweights, as mentioned above. Then you have to mill the piston tops too. Tom Hoover came up with all this back in the mid 70's when there were no 360 pistons available. Today, there are 4011 choices of 360 pistons.