Interesting read, thank you for the info. BTW, I'm a new member, and a new owner of a 76 CB 750 F, and on a recent ride my starter wouldn't disengage after the turning over. I was a few blocks from my house, luckily, and after tinkering with it on the side of the road I ended up going home and getting to work. After a week of messing with the solenoid, including incorrectly attaching one of the hot wires to the neg post killing my electrical for a few days, I finally noticed the push button on the start was broken.
Upon disassembly I found an exploded switch with bits of plastic switch housing. So, I rode down to my local indy bike mechanic and they let me dig through some boxes to look for a replacement. I ended up finding the housing (for the actual switch, not the whole assembly) from what I think was a 78 500 assembly. It was much thicker off white plastic as opposed to the brittle clear stuff I found on my bike. Only problem was that the hole the screw goes through to screw it to the assembly was on the opposite side.
So, I reassembled the switch, pretty much how you explained, and then took a small metal scraper tool and heated it up with a propane torch, and melted off the tab with the hole. I put the button through the hole on the assembly, and hoped the handlebar would hold it in place... Which, so far, it has. It feels a little shaky in there, I can feel the slightest bit of give when I start the bike, but so far no problems, the bike starts when I push the button and the starter disengages when the bike is running. I've been thinking about going back and getting a couple more of the switch covers just in case.
My only other option was purchasing the whole assembly (aftermarket) for around 50 bucks from a place called 4into1.com, which I ended up returning without even opening. I'll let you know if it gives out on me but so far, it's been doing fine. The only mishap was, that night I went out for a night ride and my headlight stopped working. Next day I removed the light from the bucket, unclipped it and then reattached and replaced it, and now it works again.. I'm wondering if something having to do with the start button being connected to the headlight because of the 'always on' thing while running may have something to do with it. Guess I just have to wait and see if it happens again.
Anyway, justed wanted to add my 2 cents and my solution incase it ends up helping anyone.