I think 20's would look good on the rear. But, of course Roger has to do what the owner wants. If 19's look good on the rear of a Camaro, a 20 wouldn't be too big on the rear of a Chevelle being a bigger car and all. I also understand the logistics of the ride height too. Just my opinion though. It's going to look killer either way.
By the way Roger, when are we gonna get some pics of the frame?