Hey Delta.... sounds like a fun project.
Kaz..... not everyone needs 1:1 thrust to weight
The wings do the lifting...the engine does the pulling. Engine power to weight is important... and prop selection is important too There is definately a lot of wing on that B-2, and its not exactly a 3D machine. There are a lot of scale modellers who can tell you of flying 10 lb P-47s and 12 lb P-51s on as little as a .61 (back in the days when there were few other choices).
The Thunder Tiger engines are good products and a good value. I have been pretty pleased with them.
The ST90 is a good, reliable engine with good power. You would not be disappointed by it. Just take the time to break it in properly on the bench.
The OS91FX is a good engine as well, and set up properly is a bit more powerful ...... although some folks on here, for some reason, have had a number of problems with them. I guess I got a good one for testing. Others have had major difficulties.
Both of those engines are "60" size cases. Both will respond well to installing a Jett-stream muffler down the road, if you want a bit more power/speed.
And.. Thunder Tiger actually does have a .91Pro aircraft engine. Very similar to their 91 helicopter engine. Its just not available here in the US yet for some reason. Perhaps soon.
One word of caution. Use published HP numbers for very-broad reference only. They are often not really suitable for comparison.
Bob