Tweety,
#1... Yes, if the entire housing is missing, I'm pretty sure you'd need it for the conversion kit to bolt up. I'd give Moss a call, their tech guys should be able to confirm.
#2... If you're sticking with the Zenith, and if CA smog allows it, I'd suggest a manual choke rather than trying to rebuild the auto choke. That auto choke is the devil!
That said... I see VickyBrit sells the kit for $130. (can't find the Moss price.) That'd get you almost halfway to an aftermarket carb conversion, or more if you need to order the choke housing as well! Or, as others have suggested, you could probably buy a single SU to adapt, with money left over for a rebuild kit.
How much modification does smog allow? And/or how much do you think you can get away with?
