1. If he wants to collect only and not driving it: Buy a #'s matching survivor or a fully restored #'s matching car. The more documents the better and the higher price.
For the 80K, I suggest an AAR or a 440 Six-Pack. A 340 nicely equipped by the factory is great too.
Do not think he will take it out each weekend. He will end up telling you that the car is too good and too rare to be driven. It will end up in the garage forever, like mine...
2. If he wants to drive it and does not really care about numbers, tags and old faded paper sheets: Buy a 440 Six-Pack or a Hemi, that will give him the most fun and tickets.
Or, and this is the best way: Buy both !