Regarding your first question regarding powering the "poke" with the Magmun 52. Mine is powered with the O.S. 52 4 stroke and IMO is a perfect match. The Magnum should be the same.

A couple of tips you may want to consider:
Either replace the lite ply engine mount with aircraft ply or simply add 1 additional mount made from aircraft ply. I have found that the the blind nuts tend to pull themselves through the softer ply and the engine loosens up some. Not a biggie, but it's easy to do and improves the engine mounting.

Make sure you strengthen the wing mounting struts with pins, toothpicks or something similar. If the joints in the struts (cabane) aren't perfect, eventually the plane may suddenly morph into a lawn dart. There have been earlier posts on this topic.

All in all, it's a great plane (pardon the pun) and a good flyer. I really enjoy mine and still fly it frequently after having built it several years ago.

DaveB