Been flying a mag 28 on a combat plane with a 10x4 apc. Little slow but pulls well. However I have another hat trick R/C choker with a 64" span and a mag 28. I also have a mac's header and quiet pipe for this combo. What is your recommendation for a prop on this combination. I understand that the pipe performance is matched to a specific prop/plane combination so I'd like your opinions on the prop so I can max the pipe to it. Thanks.

I'm by no means an expert at this but I would try a 10/3 apc then I would try dropping to a 9/? for RPMS.

I ran the MAS 9x4 GF/2 on the Mag .28s in combat. That prop allows the engine to rev up. What prop you use is going to depend on how you want the plane to fly though. But don't be afraid to try a 9x4. The smaller prop really allows the engine to turn up and move a lot of air.