Wow, this must be one of the longest running threads on here - almost 6 years to the day since it was started.
As for your mods, well, I say go for it. Just about everything else has been done to this fantastic little plane. I'd recommend the four stroke over the brushless, but thats just my biased opinion.
It seems that some need nose weight, some don't. Mine needed a couple of ounces on the firewall with a .25.
I wouldn't bother with the retracts, but each to their own. The plane already has a fairly high wing loading, but its fine as long as you fly it fast enough
Good luck and let us know how you go.