Having responded to your other note on adj pads....I'll second my suggestion to go visit JS Air Cushion stocks...and talk to them about all of this stuff...
But if you look at the XS Skeet with no adjustable comb - the comb is higher than the gun with the adjustable comb gun - when the adj comb is all the way down, flat in the cutout. This allows for adjustability both up and down from what Browning thinks is the "neutral" position.
Like you - the gun with no adjustable comb - fits me very well ---- but I shoot the adj comb versions, for more precise adjustabilty up and down ...and any cast on or off the stock. Its just a better way to go.
Options:
a. Wood Rasp to the comb ...NO....
It would be like sideswiping your car into a pole....( leaving a scar - that is near impossible to blend into the rest of the stock ).
b. Cutting the comb for an Adj comb insert ...with a bandsaw jig is the way the pros do it ( or maybe CNC machinery )...
c. In extreme cases - the gun will have to be re-stocked because the shooter is so far out of the norms / only a custom stock will work ( exceptionally short necks, very long necks etc ..)....
but I think ....JS Air Cushion ...will have a good solid option for you ...and relatively inexpenisve ...( once the gun fits ) / your success potential will increase significantly because right now you know the gun doesn't fit...