I want to build one of these, either with a Trailblazer straight six, or some sort of LS engine, 4.8/5.3/6.0. And looking bone stock like a brochure ad, with small hubcaps, body color painted wheels, whitewalls, plastic on the seats, all that. I would splurge for an AM-FM radio (which for a '65 is not easy or cheap to find) and a factory vacuum gauge. Otherwise it would be done cheaply, neatly, and cleanly and it might take me a decade to do it right but it also won't cost me twenty grand lol
Occupant: Stay away from the straight 6 from the Trailblazer. You can get better mileage and better performance out of the 5.3.
They're also a lot cheaper... I like the idea of doing an "oddball" conversion and the Atlas 4.2 has found its way into a number of classic cars to replace flathead and ohv sixes and has done quite well.