First of all, good luck in your search. And in my estimation, which is worth exactly what it costs, it's smart to make it a search, the more extensive, the better.
I'm looking too and so far have seen and driven more than a half-dozen cars. What I'm finding is, frankly, a lot of overpriced crap. I'm willing to pay toward the upper end of the scale for a proper, very nice '02. I've not found any of those. What I've found have been 40-year-old cars that have not seen any love or upgrades at all. Oh, I did see one very original car with braided-steel brake lines, but it needed brake pads, a suspension rebuild, a new interior and its engine was very soft. Oh, and there were traces of rust, even though the car is, and apparently always has been, here in Kali-Fornia.
What I'd expect to find for $8-10k, which is my budget, is a very nice car that already has had everything done to it. Period. This isn't my arbitrary number, it's from the pricing guide Sports Car Market puts out. I've found several quite untainted, dry, original cars in that price range. They'd make great starting places, I suppose, but have been priced at double what I think they're worth. When you add up the cost of paint, interior, engine and chassis (which includes suspension and brakes), you're looking at a whole lot of money that would need to be spent before you had a truly usable car.
What I'm seeing (and your experience may be very different from mine) is that apparently these cars have not received the levels of love and respect as, say, vintage Porsches, MGs or other classics. Perhaps that's because recognition of the valuable and classic nature of these cars is late in coming. I don't know.
That's not to say that there aren't great cars out there, because there are. I attended a Vintage BMW gathering here in the LA area a couple months back and there were many delectable cars there. None of 'em for sale, as far as I could tell.
So for what it's worth, I'd strongly suggest that you do NOT jump on the first car you find. Shop carefully and hard, and don't buy a car until you know for sure that it is indeed the one you want. Do whatever it takes to obtain a prepurchase inspection from someone who knows these cars. Or better, see it yourself, and take a set of mechanic's rubber gloves and a flashlight with you so you can really inspect things while lying on the ground, looking closely.
Oh, and on the headroom issue? I'm 6'4" and have plenty of room inside, even with a sunroof. Recently I drove a car with Recaro seats from a 320i, however, and found the headroom to be insufficient. But i think that 6'6" might be pushing things. All the more reason to see, and drive, as many of these cars for yourself as you can. But that's just me.