Russ,
We recently flew a Gripen on the Simjet 1200 (older version @ 14lbs) and I was extremely impressed with it's performance. No problem hitting the 150mph mark nor the 500ft field (assuming paved) although landings take a bit of practice to learn how to bleed the speed off properly. If you have a fairly smooth run-off for the first few flights you'll be happy with this combination. Personally, I thought this was a better match than mine with the P-80 due to the lighter wing loading and less residual. Any of the power plants in the 14-19 lb range will hit the mark your looking for with this airframe.... Know of one currently being fitted with a Artes Bee that will be flying off the same length runway...
Regards,
Todd