Those carbs are pretty varnished and gunked up. They're in need of a good, deep cleaning with an ultrasonic cleaner.
You'll definitely want to clean those slides, the bores in the carbs, and get the crap off those needles. In fact, you may want to just replace the needles, but it's hard to tell just from a picture.
For spares, start with David Silver. If no success there, then go to Randakk's. For O-rings, bowl gaskets, jets, etc., use only OEM Honda or the replacements available at Randakk's. Don't bother with any kind of "universal" nonsense from other suppliers. Trust me on this.
I'm not sure about the rail on the bottom that you mentioned. I'd buy a Hayne's manual for the SOHC-4's and start reading (manual available at Randakk's).
You have some work to do (and it's going to cost you some money unless you're planning on riding it for exactly one ride and selling it again), but it's workable.