The 063's a closed chamber large oval port head from late 1968,all 1969 that came on 396/325 & 350hp and 427/385hp(in pass car) & 390hp(vette) were listed as having 100cc chambers. But when my machinest measured my 063's and they were apporx 98-98.5cc per each chamber after they were mildly milled for the first time from a virgin state. But i dont know how much the mild milling reduced the chamber size.
But note that in early 1970 the 063's were only used on on a very limited # of 396 & 402 motors as far as i have ever seen or read in GM literature. But it could have been used on the 454LS5 390hp in very early 1970 but most of thoses got the 290 heads which were basically exactly the same as the 063's.
The 063's a great street perf head for mild to moderate perf use that seem to be able to support well over 400hp approaching 500 hp from all the posts i see in this site and magazine articles too but the post here are the real world when it comes to believeable #'s/stats.