Super DUKWs existed only in prototype form, from memory there was a
post war 6x6 from GMC with a 302 and later 8x8s with twin engines in
the 50's, plus numerous research modifications like the hydrofoil DUKW.
Most of the prototypes ended up in US museums in or out of the D.O.D.
Fort Eustice (Eustace) comes to mind for some reason.
If it has six wheels and a GMC 270 in it it is a standard unit and
probably the easiest to work on, TM's for the others would be available
from the Pentagon Library. Check with Hank La Barbra who is listed on
the main MVPA page, and / or Steve Greenberg in Portland, Oregon, and
Bill Keen in the Georgia GPA (I think)
If you cant find plates and it does have six wheels, check for the
chassis number amongst some bolt heads on the passengers (right) side
of the chassis between the intermediate and rear axles (yes you will
have to scrape for it) It will probably say GMC DUKW 353 XXXXX.
Hope this helps
Gordon McMillan, Gorinchem, Holland.