I've owned dozens of '66 Barracudas and still have three of them. The main expense on restoring them is rust. If you have to replace floors, frame rails, crossmembers, quarters, etc, the price goes way up. Nice front sheet metal is getting kinda scarce, but, not impossible to find. The '66 Valiant uses the same front end except the grilles and moldings. Most of the interior parts are available, as well as drivetrain parts. The best you can do on "matching numbers" is an engine with a casting and build date, before the car build date. It should also be stamped B273 on the upper front part of the block on the driver's side, right under the head gasket seam. It's usually an uneven stamp, so as long as the numbers are evenly spaced on the same plain, don't think they've been added poorly. As mentioned, no VIN is stamped on the engine. The transmission part# stamped into the driver's side pan rail will get you narrowed down to the year. It has a build date too that should be before the car build date (which is the first part of the shipping order number.) The vinyl top option on the one you're looking at is fairly rare, but, in book, not an attractive option. they just trap rust. It wouldn't put me off getting one however, just not something I would go out of my way to get. I've had two of them over the years, but, both are long gone now. Column shift isn't worth as much as a floor shift. Same goes for buckets vs. bench. Performance options add value to the car if it has any. The RH fender shown looks to have a Formula S emblem. If the car is an original S model, it will have a 7 under the f on the fender tag. There are a bunch of other codes on that tag we can decode for you if you can get those off the car (hopefully it's still there!) From what I can see in the photos, it looks like the wrong seats are installed in the car, but, maybe the originals are in the pile in the back seat? Why is it sitting so low in the front? Flat tires? Sunk into the ground? Looks like the seller has another one there in the background. Is the one he's selling a parts car for the one he's keeping? If so, he's probably cherry picked all the best parts for his. In conclusion for this long winded response, look hard at the rust issue, as there are other ones out there that might be a better buy in the long run even if you have pay more initially for a relatively rust free one. If you don't mind rust buckets, I know of another '66 V8 4 speed car not far from you. Might at least be a good donor car for you and/or your pops.
