The 478 V-6 is a Power House. It will be way more than you will need but, as mentioned, would be interesting.

I drove a 478 in a '62 GMC 6500 for 3 years.

BTW, do you have any pictures of the '66 Semi? I'm wondering if it is a Conventional Cab and what Series it would be.

Bill


'60-'72 Chev/GMC Fan
GMC 9500 Fan
Detroit Diesel Fan