The parts books are usually fairly clear with their 'up to' & 'from' dates so without seeing the book it's hard to tell just what it means.

The 1200 GX used only one part number for the cam from start to finish.

My tune-up book fortunately lists the valve events for the stock & GX cams, but does not mention if the measurements are taken at the lifter, or the valve. It does however nominate the "Valve clearance when checking the items shown in the chart"
The clearance of 0.35mm for the two cams in question would be irrelevant if the cam event check was done at the lifter as per insustry standard.

They are listed as follows.

One carb-use std cam. 13001- H1000
Working angle [duration] 248
Intake opens 14 BTDC Intake closes 54 ABDC
Exhaust opens 56 BBDC Exhaust closes 12 ATDC
This means that overlap would be 26 degrees.
Valve lift 8mm

GX-use standard cam. 13001- H2300
Working angle [duration] 256
Inlet opens 20 BTDC Inlet closes 56 ABDC
Exhaust opens 58 BBDC Exhaust closes 18 ATDC
Overlap would then be 38 degrees.
Valve lift 8.4mm

As can be seen, the GX cam is hardly a fireball grind & would in all probability work just fine in a stock 1200 single carb engine.

For the record, the A10 engine used an even milder cam.
Duration 240 degrees
Intake 12- 48 degrees.
Exhaust 50- 10 degrees
Overlap 22 degrees
Valve lift is not shown.

Even a stock 1200 cam would put a little pep in the step of an A10 as the step up in specs from A10 to 1200 is about the same as in the 1200 to GX