Can a 955i single side swingarm be put on a Daytona 600?

in theory yes, but in practice no one has done it. Depends on the following. pivot points on the 2 swing arms, have to be the same width, Altering the frame to fit is not recommended but using spacers is. The daytona 600/ 650 have 2 internal locking collars behind the outer fixing bolt. the outer of the two acts as a spacer with the swingarm itself. some models of triumph share parts but whether a triumph single swinger will fit will depend on the pivot spindle diameter also. larger sports bikes tend to have larger parts to compensate for the increase in power, strength being the key. Some custom builders have fitted Honda single sided swingarms to earlier fireblades, ( vfr 750/800 single swinger ) and some specials have used triumph single swingers. In short yes if everyting lines up and is the same size, no if it doesnt. Changing the swingarm will also change the bikes handling, the geometry will have changed. Best left to an expert to do.