Now if you do a project on a budget, there's inherently going to be some compromises or extra work you have to do. In my case some of the metal stuff was incredibly rusty.
More importantly the lower frame section that came with the bike had the swingarm completely seized on the pivot bolt and the bolt head was already decently rounded off.
Luckily getting the actual final drive off proved to be rather easy with no seized fasteners or the like.
One of the central elements in this project is the usage of XS-Triple wheels. Now I had seen some pictures of one guy fitting a rear wheel into a XV750, but that was it. Turns out the coupling is the same diameter and tooth-count but so far I am not sure if they fully engage.
The only thing necessary to make the splines engage was to remove the dustshield on the XS-rear-wheel, but I think for practical use, I will space the coupling out by a few mm to a) improve engagement and b) allow for a bit more clearance to the shaft.
Next step will be to build as much of the engine as possible to empty out the XV750 engine that came with the bike in order to make it easier to handle. (I already know that I will be waiting a while for some of the parts, but I don't want that to stop me from building the exhaust, subframe, etc...)