Don't bother trying to change the carbs to the earlier type. You'll have to change all sorts of other stuff too (intake manifolds, throttle cables, choke mechanism, maybe the throttle & right side electrical controls, clutch cable?, etc.).
Just take the old carbs apart carefully, and clean up all the parts carefully. Make sure you pull the pilot jets out and clean them up well.
If that doesn't all go back together smoothly, then try the Honda dealer for genuine Honda rebuild kits. I bought mine a few years ago, and they weren't really all that expensive, either. Float valves were sold separately. I bought one because I had a dribble from the float bowls sometimes, but cleaned up the old ones nicely and the leak disappeared. I keep the new one as a spare.
I've had the carbs apart on my 77 CB550K several times due to rejetting, and I've had only a single problem with an o-ring on a mixture screw (replaced with one from my spare rack). I still have my 4 Honda rebuild kits. I'm keeping them for the rebuild I'll eventually need to do down the road.
Good Luck,
Ed