There really is none.
The model started out as the T-1750, and then later changed to the T-1740. The layout is the same. I haven't looked at specs for each model to tell if one had different tank capacities or something, but they are basically identical. The last year for the 1750 was 1988 and the first year for the 1740 was 1989. When it was the 1750, it was a Saturn model, but when it was a 1740, it was a Satellite model. You may just have a rare transition model.
The door tags you mention started in either 1988 or 1989. I don't have my documentation handy, but my gut tells me it was 1989, which ironically is also the same year as the new silver VIN stickers. Can you confirm that it is a 1988?
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR