Dan,
Hello in MI.
Unfortunately, not much of a breakout between '70 Tempests & the '70 1/2 model T-37's that came out in the Spring of '70. The generally accepted number, is there were a total of 1419 GT-37's built as 2 door hardtops & 2 door posts for '70 1/2. Educated guess is most were hardtops & about 80-90% of production were 350 2bbls, with rest being 400 4bbls & 400 2bbl-automatics. If your friend's GT-37 is factory 400 stick car, it's quite rare. Even 350 2bbl '70 1/2 GT-37's seem to be few & far between, not many survived
On the white & black '70 1/2 model T-37 & GT-37 fender decals, that is how the cars came. Have parted a few original paint '70 1/2 T-37's, & somewhere in my old swapper rubbermaid tubs have a GM parts envelope with a few nos T-37 decals. GT-37 decal is same style of block letters. Unfortunately, when the low pressure potmetal reproduction fender emblems were introduced about 10 years ago, they were mislabled, should be '71 usage only.
With a Pontiac plant VIN, as big a number as you posted, I'd bet the GT-37 is very late production. Would love to hear more about.