The BIG thing about blocks from the way back years is the NICKLE
content... the stuff we ran back years ago was like jello... look
at the ring ridge you use to have.. you could never pull a piston
without a ridge reamer... now with the high nickle blocks I dont
even own a ridge reamer any more... they havent changed the design
just what they make them out of
EDIT
Thats for the explanation on the P... never thought about
that... just the P for the performance aspect