I actually received the manuals with my 89 Sunline 750C, the ones in the file section for the Travel Trailers are identical to the ones I have. The key thing is they didn't differentiaite between the TT and the TC, so you have to pick and choose what info you need from the files. There isn't much about hauling the TC in the files, like COG and weights, the sticker on the inside of the TC closet door is very accurate though. I would download a copy of the brochure from 1989 in the files section, that has most of the important specs you will need.
Matt and crew
1989 Sunline C-750 Runabout
2002 GMC Sierra 1/2 Reg cab Long bed
4.3L V6 4 Spd Automatic 2WD