Oh yeah I remember those carburetors---nasty business.
Well I don't know how you can beat the smog game--I suppose you could try to find a Weber carb and manifold, (if they make that application) and then every 2 years switch back the old carb and manifold for the smog test.
There may also be fuel injection systems in the aftermarket world.
You are allowed up UPGRADE a motor, if you want to spring for a newer model year Mazda engine, but then you'd have to research compatibility, and also how all the electronics would work.
In the final analysis, it might be cheaper to give that carburetor to an expert who knows how to rebuild them, than to try and mess with conversions in a strict smog state.
I do know that some parts of California are not as strict as others, so look into that.
Right now, a Weber conversion looks like your best shot---but you'll have to bolt on the old stuff when you go for the smog certificate.