Hey there,
When we purchased our Healey, we bought it from a similiar classic car dealership in St. Louis. It was exactly the car we were looking for and that is the only reason why we purchased it there. From what I've seen, alot of these places price these vehicles 20 to 30% higher than their actual value, and a good buffer will make (almost) any car look good. Buyer beware...
Regarding Gateway Classic Cars, I do recall one of our local TV stations doing an investigative report on a "local classic car company," so I tuned in to see if it was the one I bought from. It ended up being Gateway, although I cannot remember what it was about. Probably someone thought they were buying a "frame-off" and found rust underneath.
If you are really serious about the car (sounds like you are) and think it might be worth the asking price, you might find a St. Louis contact through your local MG club (they have a large club here) and pay them to go out and take a look at the car. If not, then I would at least fly out and see it before buying. That seems like a lot of money to spend for a potential mistake.
Good luck!
shane