Greetings Darren,

with regards to the XVS1100 parts: Yes and no. The liners are a bigger O.D. and as such the cases need to be bored out to suit or the liners turned down to fit the cases. Gearbox and clutch can be fitted to TR1 cases, but they are a different spline pattern on the clutch hub and as such you're then limited to stick with the BT/XVS parts. The starter on the XVS is inferior to what was installed on the TR1. The best starter bendix is to be found on late Virago 1100s  (the version without a spring).

The oldskool-no-hassle swap are Virago 1100 parts as they are a straight swap. Additionally those also sport a heavier crank, which might be beneficial on a sidecar.

Cheers,
Greg