I have seen the 40LA & 46LA used in planes that would typically have the 25FX or 32SX installed. The LAs are similar in weight to the small ball bearing engines. They are physically bigger though so planes with cowls might have issues.

I didn't know if you'd be more interested in an ARF or a kit but here are a few potential ARFs

Modeltech Magic 3D (definitely light enough for the LA, and no cowl)
http://www2.towerhobbies.com/cgi-bin...?&I=LXBGB0&P=0
Phoenix Sonic 25 Low Wing (no cowl)
http://www2.towerhobbies.com/cgi-bin...?&I=LXEDN7&P=0
Tower Hobbies Uproar 40 (no cowl)
http://www2.towerhobbies.com/cgi-bin...?&I=LXGPG8&P=0
Thunder Tiger Lazy Tiger P-51 (looks like partial cowl?)
http://www2.towerhobbies.com/cgi-bin...?&I=LXAVN4&P=0

These have cowls
Global ME109
http://www2.towerhobbies.com/cgi-bin...?&I=LXK421&P=0
Modeltech Extra 300
http://www2.towerhobbies.com/cgi-bin...?&I=LXRF43&P=0
Global Tequila Sunrise
http://www2.towerhobbies.com/cgi-bin...?&I=LXK422&P=0