Does anyone know if you could get a TH400 bolted to a ultra high compression 330 in a 1966 Cutlass as a factory option or would it have been added later?

 

It would have been added, it wasn't available until '67, and then only behind the 400 in an A body.

 

If it's a BOP T400 it will bolt up, but you'll have to relocate the transmission cross member back 6" and you'll need a new driveshaft. Unfortunately there are no holes drilled for the relocated xmember, but it's not hard to drill them unless you have a convertible. You will also need to modify or replace the front ebrake cable system.