13:1 Compression Pistons in 340 Small Block

You have to run an open chamber head with that piston. Period. Unless you want to cut the decks off. That's a PITA.

If you are going to run a 340 stroke engine, then you can use that piston. Just know you MUST deck the block. Period. Non negotiable. Period.

Unless you deck the hell out of the heads (which is a big waste) the flat of the piston will need to be somewhere around .040-.050 OUT OF THE DECK. That's also non negotiable. Period.

You can use that piston, get 11:1 easily with nice quench and use pump gas. That's what I'd do.

If you don't have a machinist that understands you MUST stick the piston out of the deck find one until you do. Zero deck won't work. And you'll need to mill some of the dome off.

When you are done, if it's done correctly, you have a dome of .125-.150 and 11:1 compression. If you are willing to buy the correct cam (not a BIG one or one with a ton of unneeded duration) but a cam specifically picked for that CR and pump gas you'll be fine.