I like the Yamaha triples. One thing to look at very carefully, before getting carried away with dollars/work thrown at one, is spending 15 bucks having oil analysis done. Why? Because the XS triples had terrible fuel petcocks (and if your analysis doesn't indicate you may have serious bottom end problems replace them with pingel's adapter plate and real petcocks) that would allow the contents of the fuel tank to end up in the crankcase. Many of these engines were wiped out when an owner started and ran them with fuel diluted oil.
The biggest favor you can do is get shed of all the flab but I'm not opposed to the very reliable and trouble free shaft setup. The engine actually isn't any heavier than a CB750 and stock for stock, I think the XS will walk right away from the CB.
I hate the overly complicated electrics, strip all that and simply rewire with a solid state box.
You can do 900cc's on them easy, like previously mentioned, you can get cams too.
The stock carbs that are horrible are the two piece bodied Hitachi units. Throw them as far as you can. The One piece Mikuni CV's are fine but parts are pricey if you buy them from Yamaha. I bought the two fuel "t's" that hand fuel over from one carb to the other, thru my dealer account thinking they'd be little or nothing....... wrong......... 54 bucks and that was 8 years ago. I also ordered other bits for it at the time and ended up spending a bit over 200 bucks for just a few parts.
Had I known, I would have simply built up some VM's from a triple Kaw (easy because the three way cable enrichener is one less thing to fuss with, but not so cheap to snag a set of those these days) or even adapted Mark II Amals, easy enough to put any number of other mechanical slide carbs on it.
The stock headpipes are ok with some decent mufflers but you have to keep in mind these have a flat (180 degree) crank and don't respond as favorably to a simple 3into1 header, as a 120 degree crank triple does. I've heard the Hooker pipe, although a bit odd, works well. I've never owner or ridden a bike fitted with one.
But you can easily get enough useful horsepower out of one, even using just the later stock cam and not spending large for the megacycle (about 480 dealer? last time I checked?) stuff, with just common sense tuning. I'd do the big bore before I spent for cams and then port work with a nice valve job before cams. Chamber detail too.
BTW, engine gasket sets are not cheap last time I priced them. I recall being shocked. Maybe they've since become cheaper.
The frames are very stiff, I actually "hardtailed" one several years ago so I've cut into the frames and ridden several, stiff enough and I'd think some larger diameter large bore bike forks off most any 82ish and up liter plus performance oriented bike
or even more modern USD forks
cool how that stuff is stronger, lighter, and even works better than the old heavy flimsy stuff
would go a long way to making one cafe useful, that and some good rear suspension units
good luck and hope the engine is in good shape
have the oil checked out, better if you do it after you have it up and running, but if you do get it running and change the oil prior, don't simply throw it away without having it checked
a before and after analysis would be great, who knows if you get it fired up and hear those mains rumbling, you may be inclined to look for something more viable, like an XS that isn't hurt