The 066 is the standard 2-core 340 radiator. The 068 is the heavy duty 3-core and is very very hard to find. It only came on cars with the 3:91 rear end or on air conditioned cars. I have a nice used 068 I'd sell, it's not as nice as a Glen Ray restored one but very decent for being an original 48 yr old part. Glen Ray can't get 3-cores new like the factory, so they take 2 new 2-cores, split one, and solder them together. They do a fantastic job with them but they aren't quite the same as the factory. I spoke to one of the guys there several years ago and that is what he told me. I think Glen Ray gets $1300 for an 068 if, and it's a big IF, he has one to restore!