Numero Uno. What you guys like the car for?
Number two. What does your son like, or is really willing to dig into?
As much as I'd want the '66, it means frame and panel repair. Depending on why he wants the car, will it be neccessary to cut the subframe for a flush butt weld, or cap it. Might need rocker work too. All pretty major stuff as you know.
After looking at the photos, its a bunch of body work in both. Won't really know how bad either is until start poking it looking for solid. The '66 didn't look quite as bad in the back as I mentally pictured.
A bunch of parts chasin' on the '65 to make it look better and more complete.
So comes down to what type of project and what he wants it for.