I'm sure you will find someone very keen to swap a Tracker for a Viscount, as others have said, Trackers are very common compared to Viscounts. Damn shame to shorten the barrel.

I doubt that many Xocet parts will fit well - the Viscount cylinder is 25mm whereas the Xocet is larger, either 27 or 28mm (I suspect the latter). A biro pen spring is a common replacement for the trigger spring.