Whats the deal with the KB 243's, good or not?

I have a long association with the KB's helping design the reverse deflector pistons for the open chamber heads
lots of good advice above
with any piston detail your heads and make sure there are no spark plug threads on the plug or head showing,
round any sharp edges
dial in your timing and tune tune tune
detonation will kill anything and as said forged will give you a little margin- but not much
do get the ring gaps right
I like ductile top rings
weight does make a big difference
I only now use TRW style for low rpm Trucks
hone with a torqueplate
do the oil mods
clean
enough