I have no idea if you can use the key tumbler. But what I do know is that every euro golf 3 has a licence plate tube like this and every golf 3 na has a tub like the one you have on your cabrio. So all those people (in the usa) with euro hatches and all those (in europe) people with na hatches seem to found a way to fit it.
Sounds like we have the same question. The issue is going to be if those of us with old-style tumblers can install them in a trunk lid that came with a new-style key. It would be the same question we'd face if we upgraded to the US-spec 3.5 hatch.
I'll try to see if I can dig up the answer on one of the forums.
So, with the 3.5 Cabrio its just the bumper, not the rear hatch that is different? Then, with the MK3, it is the hatch and rear bumper that are different? Just curious as I have a Cabrio 3.5 VRT project that I would like to get set up with euro bumpers and rear hatch if they exist, any connections on any sort of front grille options for the 3.5? Pictures are always good.
BTW, I think what you are doing is awesome and I am sure it is very much appreciated.
Bump because mr Polizei has been very forthright so far, looking forward to receiving the reddish purple hatch! Yummy. Hatch will be replacing this one, which is shaved but the shave job cracked around the license plate bucket like i knew it would eventually.