C6 has to me very destinct casted ribbing on the top that leads up the bellhousing, like 5 small ribs. I think the cruise had a bellhousing that could be removed whereas the c6 didn't. The c6 has 17 bolts to pan and the cruise o has 15. OK, i found my #'s book, so for 1968 if your car has a c6, the casting # has PGA- or PGB- , and the cruise o has PFA-A or PFA-B OR B1 or PGA-A2. The only engines to have the cruise o matic were the 240 PI, 302 PI, or the 390 column shift. Hopes this helps.