ORIGINAL: Prekin
Hello erec,
I have experience with the Zero 50 CC. But every CMP Zero needs a lot of weight in the nose, so the better choice is probably the heavier engine. For my bigger Zero I used pneumatic retract for the ESM La-7. Maybe you can compare some ESM retract, for example Ki-84. I don´t have any experience with any electric retract, so I can´t help you with this question. CMP models don´t have scale length of the legs and diameters of the wheels.
CMP has two Zero planes. Your is bigger one (for 50cc), but I think that erec11 has smaller version of same plane.
erec11, I have Zenoah 26sc with magnetic ignition (lot of needed weight at front) and it came at 8.5 kg empty. Till now it has only 3 fights,
because it was finished at the end of flying season, but for now engine has enough power.