340 compression ratio

what is best - depends on what you want to do with it. and as said above piston can be changed and so can crankshafts. The thought is if someone changed to a steel crank or even a 0 balance crank then chances are other are also changed. if it still has the stock cast crank and balancer assy with the 587 heads then perhaps it was a more stock rebuild and a stroke of 3.31.

for what mark is speaking about requires removal of cyl head, if going through that take it to a machine shop and have them do it. it is cheaper.