I'm not a fluid engineer either, but I've rebuilt enough zeniths to know how easy it is to get it to be less than perfect.
The kit is indeed, one size fits all. But you can still visit your favorite parts supplier to get a few extras. For instance those base gaskets. Throw away the ones from the kit and buy new bakalite spaces and metal plates. That will keep aways the leaks for a few decades.
For the accerlation pump that seems to leak, did you buy a new one (strongly recommended) or did you attempt to replace just the skirt (You're a guy, what do you know about putting a skirt back on
)?
The linkage parts should be replaced from another carb if they're worn. There is no way around this. You can probably find another set of springs too, but ask the dealer for them (can fast line get dealer parts?)
I long ago stopped cleaning my carb parts myself and began handing them over the a professional shop. They will grumble, but if you ask nice, and promise not to ask for any technical advice, they'll do it and that means a rainbow coating on the potmetal. Be sure to take the time to check for flatness and correct any issues before that level of cleaning, since it can cost you (the toxic waste isn't cheap).
The fun part with the zeniths is getting all the stuff outside the carb in shape. The dashpots, fuel return valves, choke settings, etc. That stuff you handle one sub-system at a time. Each has a bench setting to work with and a way to test it once the car runs.
If you want to switch carbs, there are nice webbers that bolt on once you have an adapter plate. Also you'll find that the unimogs (trucks) had straight 6 motors with a single carb. One of their manifolds would be the start of the conversion.
At present, I don't have any cars with zeniths, but I seem to have one of everything else with a fuel delivery problem. such as it goes. I picked up a set of ford escort throttle bodies way back when as study of how to do TBI. While less efficient than multi-port injection, you can't beat throttle body injection for cost and efficiency, presuming you can get the electronics to do the right thing. One of these days I'll get to that project. There's always an M110E or M114E motor with D-jet. Those are factory supplied at least.
-CTH