The old Hayes Slimline tanks are still being made:
http://www3.towerhobbies.com/cgi-bin...?&I=LXK835&P=7
They were designed to fit in slender fuselages using nose retracts. Check the dimensions of the tank above. It might work. If not, the 8oz one probably will:
http://www3.towerhobbies.com/cgi-bin...&I=LXK834&P=SM
David