Yes, of course GP recommends the Fuji engines, but even the manual for the first "Performance Series" plane (the Ultimate) mentioned the use of a DA-50! I don't think that they are oblivious to what some modelers are using.
As for where to send my money, I guess I'll answer my own question...
http://www3.towerhobbies.com/cgi-bin...?&I=LNUSE0&P=G
You might notice that the title even implies 50cc (not 43cc) gas!