I have 2 sets of heads. One is 3932411 and I believe mortec said 1.94 ,1.50 76cc. The other set is what im confused on. they are 462624 I am finding very conflicting answers, I had these on a fully rebuilt motor that ran for about 1 minute but then could not figure out why it quit running. Maybe this is why. that casting number is said to be a 305 and 350 casting number. the 305 valves are 1.94,1.50 76cc and the 350 valves are 2.02, 1.60 76cc. How am I able to tell which set I have. And if they are the 305's would that have caused my 350 to not run? I am looking for new heads for my truck and although these are not the best, it is what is available to me. Thanks for any help.