I had one with a couple of different engines in it. The .91 4-stroke will be fine-sounds better. The plane needs down thrust or the trailing edge jacked up to lower the incidence or I guarantee you it will climb like mad on full power. You'll trim like heck to keep it level. When you reduce power, it will dive because of all the down trim you added. In my opinion, the plane is poorly designed from an incidence (wing and tail) and thrust line standpoint.

A buddy and I built 2 of the smaller ones and one big one. On the second small one we jacked up the TE 3/16 inch and it helped, but still climbed somewhat. The big one had a .91 4-stroke and an OS 1.08 in it. It cruises around at slow speed OK.

If I was doing another one, I would put a full symmetrical airfoil on it. Then you could set 0-0 and fly like normal. Since the original full scale had the very thin under cambered airfoil, any thick airfoil is non-scale so you may as well use a good flying one.