They are too far down in the hole and have a HUGE valve canyon , err , valve relief. If you don't have a head with close to 80cc chamber and deck the block to bring them up in the bore you end up with less than 9.0 compression.

By the time you pay for all that machining you could have just bought a piston wit ha higher compression height.

The speedpro LF2315 is a good piston but it's HEAVY and it has no valve reliefs.

The best choice for a 383 is the Diamond piston , but it could stand to be a little taller CH than it is , the good thing is you can have that adjusted by them for not a lot of dough.