If it's a '68, then it could be in all likelyhood a 289 with 302 heads. '68 was the transition year and it could have come that way from the factory. My '68 had 289 badges, but the engine was a C8. Wrong engine, or wrong badges? Maybe neither. I've heard of C8 blocks being built with 289 rotating assemblies from the factory, at least until the parts were used up.
The other possibility is that the heads came off some other 302. If their part # is C8 anywhere, then they are either original or at least of the correct vintage.