FWIW, I have the 1.08 on mine...nice combination. I side mounted it and use a Bisson, Pitts style muffler.

A friend has a TT 1.20 for his...that's a good engine, and less expensive than either of the 2 you mention...but it is a little heavy.
(so is my O.S. 1.08 though )
He hasn't flown it yet, so I can't report on it's power / flying qualities.

The Webra 1.20 is a good 2 stroke, it's light, and "only" about 200 bucks...I have flown a couple of Funtana S90's with those on them and that's a nice combo too...might make a good engine for the ST?