Both Zenith AND Tillitson carburetors are very good carburetors. As Zenith is cast iron, they generally do not warp. A great many Model A drivers, while liking the Zenith, find that the Tillitson carb. performs a bit better and has good reliability. The weakness of older Tillitsons is that they are cast from 'pot metal'; an excellent material for a reasonably long time - but not so good for a long time of aging - warping between the two halves sometimes becomes an issue. Not a critical one, as some file-matching is an easy fix.
I have used a 'properly rebuilt' Tillitson carb. with excellent results for over twenty-five years, and am very happy with it.
I also have (on another Model A) used a 'properly rebuilt' Zenith carb. for over 50 years, with excellent results, and am very happy with it.
As has been said, the Zenith carb. is what Ford had designed and built for use on his Factory cars. Tillitson is what was widely used as an excellent replacement carb. for over 80 years - so it IS a very good and well liked replacement carb. If it is a 'show car' that you are concerned with, then a Zenith is a MUST. Otherwise, either carb. will work with excellent results. In the end, it really becomes a matter of owner preference, prejudice, and past experience. But with your post saying " I want to go back to original as possible", I suspect that you will want to go with a good rebuilt Zenith carburetor.
- Doug Vieyra,