ROO & Grass
Bob- As long as your grass strip is well maintained eg flat and cut, you would be fine... I am confident you should be airbourne in only a slightly longer distance than with your P-80
Also consider adding slightly larger diameter wheels all round, than you would use off of a sealed strip (less drag).
TJT reps will be attending FJ 03 and will be more than happy to show the TJT-2000 to you, and all interested jet modellers.
See you at Florida jets