Well, I picked the car up this evening with a handshake and an agreement that we were square on price.
Drove it back to my parents house(about 5 miles) with my wife following and the car was a dog. With my foot buried in it, I had a hard time getting to 40mph. I was running down a 55mph road in 3rd gear hoping I could just keep going. I also could not get it to idle.
Get home, pop the hood, and plug wires 2 and 3 are reversed, something I'd mentioned to them a half dozen times(the distributor turns CCW, and of course 1-3-4-2 as on any 4 cylinder, so it's not an uncommon mistake if you're use to CW distributors and don't pay attention). In any case, I reverse them and it won't start at all.
I sat on it a few minutes, then went back out. When reassembling, it's easy to drop the distributor in in any orientation, although we usually consider "correct" on this car for #1 TDC to be the top right when looking down at the distributor. I start moving plug wires around, and finally when I put #1 on lower left(and the rest following in order) the car came to life with the most ferocious roar I've ever heard from it.
I hopped in for a test drive, and I could not hold the car back. I pulled out of my parents subdivision and was at 60mph without even realizing it. I've never driven a 4 cylinder MGB that drives like this-it was phenomenal.
I'll go through valves, timing, and mixture tomorrow morning, and we'll see how confident I feel to drive it back to St. Louis.