Paul,
I think that I fully understand your needs: a reasonably priced engine which will provide a bit more power than the LA .46.
I believe that Martin hit on the answer with the Enya 50.
Although it will cost you more than the Tower priced Tigre .51, it is an 100 % reliable engine that can even use the muffler
that comes with the engine. Certainly, one hears of instances of the S.T.'s which seem to work beautifully without further
work, many do come with flaws and problems needing to be addressed before you can fly them with any feeling of confidence.
(Of the three that I purchased, only one worked even reasonably well without further work.)
If you would like to be pioneer, you could purchase an Aviastar. I'm actually curious as to how something other than the
prototype actually works.
Of course, if you have major problems, the seller, whether it be Tower or Brodak, will be good for the return or exchange.
I, personally, don't like to screw around with returns or custom work if I can avoid it, and would be leaning towards spending
a little more for an engine with known quality control, an Enya.
It all comes down to "You pays your money, you takes your chances."
Please keep us informed how your search progresses.
Best regards,
Richard Ferrell