I have come across a few 340 MIE engines that had 2 bolt blocks, so it is possible that it is a 2 bolt.
Eddie

When I wiped out the motor in my first baja we pulled it and it was a 2 bolt block. Built a 496 out of it and studded the mains. It made almost 600hp And did not have any issues with the bottom end, it did however split a cylinder wide open one day and destroyed everything!!!

I think your best bet is to find a newer block with no chance of being rotted internally if your looking to build something requiring you to take a good bit of metal out of the cylinders!

seen many 330 with 2 bolts, have a std bore 4 bolt gen IV bare block if you need

If it does end up being a 4 bolt and I try to keep it what is a rough estimate of how much sonic testing costs? Would it still be better to find a newer block?

The block i used that split open was a fresh water motor. But unless you had a closed cooling system on it I would definitely have it checked out before building.

2 bolt motors can handle some hp,back in the day seemed like the best running motors were 2 bolts. Ran a stroked 2 bolt in the drag boat for years NO ISSUES. JOHN SR

Sonic testing $150-250.