You could start with one of these
If you buy this engine, you will need to cut the crank like on the GT1 and you'll need to buy the assoc clutch nut
Or you could try the OS .12 TG with rotary carb
and you'll need the 2312 clutch nut and you will need to cut the crank like the GT1. Tower Hobbies says the engine is discontinued but I thought they just came out with it?
Or you could buy a higher end novarossi or orion or OS with an SG crank (kit comes with sg crank nut) but you still want a rotary carb.
Its my opinion the OS engines are very user friendly when breaking them in and they are very easy to tune when they are properly maintained (no air leaks, bearings in good shape and engine was properly broken in).
If you need help on how to cut the engine crank, PM me and I'll provide details.