I am going to buck the group-think here...
His price is nuts, It's worth a dollar over scrap and that's going to be tough to get without a title. Buuuttttt... I don't think title is huge obstacle as long as the po-po says it isn't stolen, at least in my state and certainly in AZ where I titled two 5th Ave's that had been dumped in parking lots.
As to the rust... I'd much rather deal with roof rust than a bunch of structure and 1/4 panels. For a moment, let's take him at his word. That underbody could be solid as a rock. My Monaco is, but I have a bunch of ugly crap bleeding from trim edges and such. I don't see anything down low, and that's what counts.
The car itself... You could basically treat this as an empty canvas. It's a low-level 4drhtp. Swap in any formal interior or be one of the 1% of the average public with good-enough taste to pull off a good custom look. Engine swap? Hellz yeah. Hemi? Sure, but obvious. How about a Pentastar? A truck EcoDiesel. or a Cummins. Do whatcha like, paint how ya like, with no guilt about trashing something that survived 45 years.