That would be a score. it would be a 4119/4121 for a manual or a 4120/4122 for an auto. second number is "clean air package" and may have 3 stage rods with dimpled rod covers.
I have the original Carter AFB 3853S on my engine that came with my car.
The Automatic carb is the Carter AFB 3854S.
I sold a siezed/locked up 4120 at MATS a few years back for $25 as parts. I'd picked it up for about that for the choke butterfly, but it was different than the ones on the '65
