RE: mvvs.77 or .91
Micro,
The #3266 is the tuned pipe intended for the #3094 26 cc engine (glow and gas).
It adds power between 6,500-9-000 RPM and although there is no physical barrier to prevent it fitting, (with the right #3251 side header; not the 26 cc header #3265/26), your engine is designed to spin faster, so the pipe will be inefficient.
Use the #3250 and don't forget the header (they come separately; #3252 for rear exhaust setup; the cylinder and sleeve must be rotated before the engine is run).
You can also ask Jan Karlsson (JAKA) as the Swede dealer.