Sturtz, you should be fine with the .46AX especially from a paved runway. I would recommend heavily against running a heavier engine on this bird after flying mine. Just use the supplied engine mount and extend it out about 1/4 to 1/2" so you get the 4 3/4" distance required from the firewall. I used two 1/8" light plywood and glued them together to get me close enough for government work. I ended up being 1/4" too short, but that wasn't a big deal. Remember, my plane flew quite nicely up to the point I experienced the fluttering.

You may want to reinforce the joints between the wing mounting bolt plate and the fuselage sides it's glued to. They use tristock and what looks like plenty of glue, but the light balsa fuselage sides are the weak link (like someone already pointed out on this tread). Also, make sure you gap the top and bottoms of the aileron control surfaces. My gaps were tiny but in hindsight I wish I had gapped those locations (course I didn't expect the "massive" fluttering I got anyway).

Good luck and keep us posted.