I think a 3W-42I would do great on the WM GS Zero. However, you only have slightly less than 6" from the firewall to the front of the prop driver washer, so the carb of the 3W-42I will need to stick inside the fuselage. My next WM GS Zero will get a Brison 3.2 if I can still find that engine.

Here is my prop collection for my Brison 2.4: