thinking way back in the cobwebs of my old noggin, i remember "some" [?] of those type of choke mechanisms having a plate with lines on it, and those were adjustable by loosening the retaining nut and slightly winding or unwinding the thermostatic spring.
problem is, i can't remember if that was a factory unit or a parts store replacement.
also, the ones i remember like described above, were on 4bbl intakes. as cheap as Ma was, i wouldn't be surprised the basic mechanism would be similar.
a picture of the spring would be helpful to see if my foggy memory is any way near close.
i'll see if i can find any choke mechanisms on my shelves. i'm curious now about this.