So the XS2 has 34mm forks that are a bit spindly. A lot of tracker builds employ a fork brace and I'm unsure of the availability to fit one to those forks. Later model XS650's used 35mm forks that can be pretty decent rebuilt and modified - parts readily available. The triple trees need to come with the new forks. You have a 30mm dia. steering stem - same as later model XS forks, the length may need modified.
Two other options that get a bit more involved are inverted forks from other modern sport bikes and - to replicate mid-'70's flattrack racing bikes - a Ceriani front end (those often used spool hubs).
Wheels and brakes a whole other discussion; what look are you thinking about?