The necks back then were hand sanded, so it doesn't surprise me that there is some difference in dimensions from guitar to guitar.
That's true but I don't think it was to the extent that fretboards that were 1-11/16" wide got narrowed down to 1-5/8". Both of those were "standard spec" on different fretboard widths and lengths.
Suspect yours is a tiny bit narrow due to the individual final shaping by hand.
This accounts more for variations in neck profile between any 2 guitars even though they had target templates.
The message for our OP is that no two necks from Westerly were absolutely identical unless "by accident."
It sounds like the 1-5/8" necks you mention, Bengal, are on 24-3/4" scale ("shortscale") necks, that wasn't an unusual combination for them at the time. (can't remember what scale has been cited for that year but Tommy should be able to confirm. Long scales on F30's numerically are the exception rather than the rule, but I think they went back and forth twice over their entire history.. I think that '78 below with the F50-style fretboard was the first time they went longscale [in '76]. Sorry I'm just fuzzy on specific stop/start dates)
Or as previously mentioned, we've seen evidence that Guild would simply build a "batch"' (term used loosely here but possibly true in the technical sense) of guitars with an "off-spec" nut.
We know they did this on an actual "run" of D40's in '64, they got 1-3/4" nuts and flat-radius fretboards when the spec was for 1-11/16" and a shorter (rounder) board radius.
Another recent example was with the G37's previously mentioned, 2 guitars (with s/ns within like 10 digits of each other from '86 or '87) from different owners reporting 1-5/8" nuts seems to imply they did a run of those with narrower nuts, when spec was 1-11/16" on those as well.
Generically the 25-1/2 scale with 1-11/16" nut seemed to be the most common for all flattops overall, and 1-5/8" was more common on shortscale instruments, which tended to be the F- and M20's and F30's.
And finally, just when you think you've seen everything, along comes an oddball you're convinced can't be factory original until Hans comes along and says it is.....:glee: