Hope I can shed some light and not confuse this further:

Many things changed year to year, an identification format that was used in 1973 may have changed in 1974 or any other year.

First, TZE 166V902114 is NOT an odd number, it is an invalid TZE number as well as not a 1976 model (TZE166).

The #902114 is the order #, can also be found at the top line of the service parts sticker on the glove box & other paperwork if you are fortunate enough to have the original build sheet.

Dave Greenburg & I tried to make sense of much GMC information, order #s were all over the place and with no apparent order to the #s we eventually gave up. We did determine the following:
1973 & 74 order #s appear as 9xxxxx
1975 to 78 " " " " Sxxxxx (first 100-200 in 1975 appear as S5xxxx all others S0xxxx)

1973 or 1974?
The highest 1973 TZE# I have listed is #3035 with a build date of 11-01-73
The lowest 1974 TZE I have listed is #0020 " " " " " 11-12-73
Since the glove box sticker is missing, the only way to tell for sure is the frame stamping found drivers side below the "sink" window (see my album for a picture).

VIN tags on the firewall:
1973 & 74 tags were rectangular, higher than wide, the screws holding the faux firewall tag appears to use the original holes.
1975 to 78 tags were also rectangular, but wider than high. All genuine tags should have the numbers embossed and mounted with special rivets.

Why the replacement tag, don't know except why would someone do that....... unless to deceive.

What year? My guess is, a very late 1973
My reason, just because ;^)
Bill