First:

You have the perfect combo on the LT-40. I had a LT-40 that I put 13~14 different engines on, the best I found was the Saito 50 and the LA40, so your Mag 52 = my Saito 50. The LT-40 doesn't like to be overpowered.

On your stick, they can stand overpowering and a tail-wheel so I'd go with about a 60 size four-stroke.

4C vs. 2C that's personal so do what you enjoy, I personally like the 4C most the time, but on something like a Diamond Dust there's nothing like a 2C with a pipe.

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