"Surgery" may have been a bit too strong. The first two "Whiskey" airframes,
162532 and 162533 differred from subsequent "production" deliveries, starting with 162534 around the exhaust area. The "cutout" forward of the exhaust nozzles is filled on the "non-test" versions. The "cutout" was an original feature of the exhaust nozzle IR cooling system. Oddly enough, 162536 which was delivered to HML/A-169 had the "cutouts". I have photos of 32, 33, 34, and 36.
161022 was the "proof of concept" airframe (modified AH-1T). It also had the cooling "cutouts". Since I was just getting back into building, I didn't feel like tackling even a "minor" modification.
There's lots of little nit-pickey differences between the two test (what I call prototypes) vehicles; ie. no cable cutter on the chin, and the airframes delivered to the FMF. All of the references I have after 1989 show the "Whiskey" with the "updated" exhaust configuration. I don't have the intimate knowledge of the "W" as you seem to have and need to rely on reference material at hand. I could be wrong, but I just can't find a Desert Storm or OIF photo of a Marine "W" with the exhaust cutout as molded on the Italeri kit.
Even their 1/48 version, which has Desert Storm box art, has the test airframe configuration. An early kit review contained in a rival publication points out the "problem"
with the kitting of the early production version versus the version delivered to operational squadrons. Fine Scale did a review in March 1993 of the 1/48 version, but I can't seem to find it in this disaster I call an office.
Don't mean nothin'