I'll give you a response, but i must preface it with the fact that i haven't had any "current" experience with off the shelf converters. Some may have gotten better, some worse?
First off, i'd take the Sat. Night Special off the table. That type of conv. is not much different the a stock one, and i think you'd be disappointed with the results.
My only personal experience with a TCI was working on and a few dozen passes with a friends street/strip 12sec car that had a Super Street Fighter 10". Never had any issues with it, and it was surprisingly consistant at the track. The only minor problem that i didn't like was that it was very soft in the cruising range, 2000/3000 rpm's. This car had 4.56 gears, so i can only imagine with a 3 series gear, it would have been "really" soft.
Most of the shelf converters use average setups for the innards and are not real efficient. They get most of there stall speed from a reduction in diameter.
The only other thing that i can add is, with similar off the shelf ATI & B&M street stuff, behind small blocks your stall speed will be at the bottom of the advertised range.
I'm not trying to discourage you, but i believe a custom build in what your going for is not as expensive as you may think. A couple of extra bill's may be money well spent.
