1970 340 has the 1973 low compression pistons

I would build that like this.....LEAVE the 4 eyebrow pistons in. Blueprint the engine to 9.2:1. Put the Comp XE268 in it and it'll haul *** and you'll never, never have to worry about the problems with high compression like spark knock, kicking back against the starter or any of that "nonsense". The difference between compression points is about 3%. You don't want a 10:1 plus motor with iron heads trying to fight detonation.