Help with 1981 trim codes

Guys I'm looking at a 1981 Vette that is silver over charcoal two tone with a red leather interior. The car has a red and orange stripe that runs around the midsection that divides the silver and charcoal. The stripe is also on the center of the hood of course.

I have never seen this color combo (red/orange on silver and charcoal) before and cannot find another like it on the internet. Is this an original factory combo? The trim tag has the following numbers:

74I 33L 33U 39M E

One site I visited said that the two tone silver over charcol exterior should be 33/39, that would explain one of the 33's and the 39 but what about the other 33 and the 74? The interior numbers that I found for 1981 Vettes do not list a 74 or a 33 for any of the late model C-3's.

Also what do the letters mean after the numbers? Is there any way to tell from the trim code if this car in fact came with the red and orange trim?

Any help would be appreciated.

Thanks