[C10 - C90 Bill]

I like the '66 C-60 best in the Craigslist ads that you posted. A 4-53 would be more what GM put in there and a 6V-53 would be one step up. Still could be a challange to fit it in there though.

They put 6V-53's in some GMC 7500 Tandem Axel Dump Trucks, therefore it should pull your Gooseneck Trailer with no problem.

If I were to put a Detroit into a '66 C-60, I myself would be looking at a 4-53T.

To have a 6V-53 in a '66 C-60 sure would be unique, but an alternative would be to buy a truck with one already in it. They put a lot of them in '66 and up Chevy C-70's and GMC 7500's. I would also consider a Chevy C-90 or a GMC 9500 with a 6-71. You could also get a 6V-92 in a newer one.

Bill