The Zeniths that you have are the best of the Zeniths used on Alpines, so please don't bin them if you decide not to use them! The big problem with the Zeniths is the throttle shafts wear the carb body and then suck air in around the shafts. They are not hard to rebush though. Check for any slop in the shafts. Second problem is that parts for the Zeniths are hard to find. Though asking on here for a specific part is the best chance of success.
Fitting decent air filters is important, as the original wire mesh 'filters' are great for keeping rodents out, but that's about all. I bought pancake filters with foam inserts for the Zeniths that fit under the bonnet line nicely from Sunbeam Specialities.
I had my Zeniths fully rebuilt about 20 years ago and they've been fine ever since. I ended up with 130 main jets (actually drilled out some 112's) and they seem to suit the 1592 engine well. I think Jarrid Gross recommended that jet? The carb rebuilder told me not to go nuts with big return springs that put a side load on the throttle shafts. Put the spring on the linkage, not the carb (I know, a point of failure and potential for stuck throttle, but that was his advice).
Despite what it says on the carbs, check that the internal components are all the same between the two, lots of interchangable sizes on various carbs which will muck up your carb balance. I'll try to attach a chart of jet sizes if I can find it.
Good luck, let us know if you need help/parts, and of course which way you choose to go.
Cheers,
Paul.
