Brian Gardner did some ABC ' Stunt ' 35 Super Tigre piston liners .
They go in the 21/35 Ball Bearing too . . . just have to take a disc grinder to the head for the baffle slot .

Tho I think he had heads done too .
I tried a 35C ( Combat ) and a 21/35 in the olde Phantom 52 span Magnum 25 / OS 25 sucker . FSR BB 25 did maybe 10 minutes ,
21/35 did 7 minutes odd , and 35 C , still tight in the shaft , did around 5 min - on the same tank full . Thats the ' flat top ' 35 C .
The 21/35s came with a Big & a Little ( 9 mm & 3.2 mm Venturie ) The 21/35 unmuffled on a 9 x 6 theee blade sounded nice &
meanaceing unmuffled - in a damp steady 2 stroke .
The BIG Problem

if it is one , is the ' Flat top ' piston set up has marginal ' sub piston induction ' right across under the piston
at T.D.C. ,
said to contaminate the case charge Muffled , & reduce Output discernably .
So the A B C set up is the easy answer . Tho I think most C-35-S were eaerly ' Hard Liner ' and last forever . Before the Liners were less hardened for easier Break In . A bit like the Rings in all but Early Chinese STs were less hardened - were told - for easier / quicker Break In .
Reports from 21/35 Users of the Stunt A.B.C. set up appear favourable . But Weight'd be similar to the 21/46 . So where does that leave you.