wonderin what the difference between the 2 castings? pulled 062 off motor, found set of 906's for great price, reman, ready to go, with all indications that the two castings are pretty much the same. is this right?

 

Ya the 906's have a little less flow....I think its something to do with the exhaust valve guides hindering the flow....but its not a substantial amount...they should work fine on a stock or mild motor...someone correct me if im wrong!!!