BH - I agree that the US41 can be "improved" with the larger carb and with ignition, but then it gets lighter so you will need to add weight. Have you looked at a used Quadra 65 or 75? Way too much power, but the muffler is in the rear and you could limit the top end or run a multi blade prop with plenty of power to pull it.
Best replacement IMO would be a ZDZ 40RE to put the muffler in the back - add the weight you need for balance and the engine will be a good for the next airframe (when you get to that point).