Submitted by jmprnt@interserv.com
My reference material shows the following:
engine year min max 221 all 48.3 51.3 260 all 52.0 55.0 289 63/65 52.0 55.0 289HP 63/67 52.0 55.0 289 66 52.0 55.0 289 67 52.0 55.0 289HP 67 52.0 55.0 289 68 61.7 64.7 302,2V 68 61.7 64.7 302,2V 69/70 56.7 59.7 302,2V 68 52.0 55.0 302,4V 68 52.0 55.0 302BOSS 69/70 57.2 60.0 351W 69/70 58.9 61.9 351W 69/70 56.3 59.7
Intake valves were 1.67 for the 221, 1.78 for everything down to the 302 BOSS which was 2.19 and the two 351's which were 1.84.
Exhaust valves were 1.45 beginning with the 221 and continuing through both '68 302's; the BOSS jummped to 1.71 and the two 351's were 1.54.
There were also differences in port size and rockerarm style.