340 changes

Anyone know what changes were done to the 340 in 72' to bring the compression down to 8.5?? I am looking at getting a 72' 340 for my 340 Demon and was wondering what I would need to do to it to get it up to pre 72' power. Also did the cranks change from forged to cast?? Thanks for any tips in advance.

Cheers,

Joe