I have side mounted my Thunder Tiger 36 by just creating a form fitting cavity in the lower corner of the fuselage. This was on a Kobra and a Sig LT-25. Cut out enough of the fuse, running the cut to the curves of the muffler to get it to fit. You will have to grind a little of the firewall with your dremel. Then fill it back in with balsa and spackeling, sand it, paint the area after fuel proofing and your are done. No expense of buying a muffler extenstion and you have a neater, tight-fitting installation.