I LOVE the Yamaha triples. I have an running 850 project, a couple good engines and a 7502D parts bike. In fact, this 850 was my first "big bike". Great motor, when in tune will pull like a freight train. head to head, the 750 will leave a cb750 in it's dust and make a good race for the GS. The 850 is just better all around.
There's a fix for the 2nd gear pop-out that can be found at the yamaha triple owners group.
Hinkley Triumph 750/900cc triple carbs drop right on and are MILES better than the stock carbs.
The header from the same bike can be made to fit with a small amount of welding, WAY better than the stock pipes, nevr mind the muffler(s) you may choose.
One of the best initial mods you can do for your bike is to swap to a 80-82 electronic ignition, it's a drop in and the bike will be stronger throughout the RPM range but will start and roll on much better.
You may or may not have Koni adjustable shocks on the back. It seems to be a little random as to which ones came with them. If you do they are worth sending out to be rebuilt, add a bit stiffer spring and you're dialed. The forks are fine for touring around, but you'll want to upgrade to better units if you plan to ride in any sporting manner.
Delta Cams in Washington can regrind your stock cams for more power by making the base circle smaller. Works great for these engines, the heads also benefit from a small amount of port clean up, especially on the small radius and around the valve stems.
You can rock 100hp+ with a bit of work and a set of 850 pistons and cylinder.
good pick!