Well, again, I recommended the Thunder Tiger F-91s originally because it is very, very close to the .75 AX with regard to weight. Changing out the engines shouldn't require rebalancing the airframe. Just swap engines and go fly. At worst, swap engines and motor mounts then go fly.

CGr. should enjoy longer flying times as well; I would expect the TT F-91s to be less thirsty than his .75 AX.

Please give the F-91s serious consideration, CGRetired. Thunder Tiger four-strokes are wonderful engines and should be more popular than they currently seem to be.