Hello TKO,

I naturally prefer the sound of a 4 cycle to that of a 2 cycle especially on this type of airplane.

I recently checked the balance of the airplane and with my 32 SX the airplane is a little rear heavy. This tells me that the use of a heavier engine would not need additional front weight. However, I would think that a 60 would be too heavy up front. I think a 46 size engine would be best.

As for 2 or 4 cycles, here is my thinking. Around the circunference of the cowling are three tabs whose holes have to align on T-nuts on the firewall.
If you use a 4 cycle there is a good possibility that 2 of these tabs (the holes) will be blocked by the head of the engine. You will then need to add tabs at different places on the rear circumference of the cowling to keep it in place. Believe me, adding two tabs is not an easy matter. I had to do it for the 32 SX, I imagine it would be more difficult with a bigger engine. Check my picture below and you can see the two extra tabs I had to add. Of course, forget about the fake radial when you add these extra tabs. There is no way you can align the tabs with the T-nuts with the fake radial in place.

Another consideration... a bigger engine means bigger servos. There is no problem in the fuselage. However, It is a diffrent story for the wings. I upgraded my servos to Spektrum's A5030 (these are minis)and I am having a hard time fitting them in the wings. I am almost there.

You are right a 60 size engine would be too much for the firewall. A 40 size 2 cycle would be a better choice even if the sound that we want to hear is not there.
Good luck and post pictures of your work.