The 1G 99 Fiberglass bumper was originally designed around a Base/ES Stealth, which actually uses the SAME pop-up covers (the black or colored panels on TOP of the popups) and the SAME flasher/snake-eyes lenses. The RT and TT lights obviously use different corner signals and snake-eyes (a single wrap-around unit) and actually have different shaped pop-up top covers, thought not a huge difference in shape, but they are different.
I know we have had some customers install the bumper on the RT body style, but have not received any pictures of the installation - process or finished product. But what they are doing is forgoing the RT corner/snakes and switching to the corners included with the bumper and either running the GT snakes or just simply leaving them off entirely and not running any - like the couople samples on our site listing
3SX Custom 99 Bumper 91-93 3000GT*-*Mitsubishi 3000GT*/*Dodge Stealth .
For the 1G RT style, you'd be honestly easier to install the factory 99 as it is already set up for an almost wrap-around style corner light - the bumper simply runs flat along the front side under the headlight to the fender where the 99 corner signal goes. Only difference would be the RT corner lights curve up at that back lower corner whereas the 99 corner light comes to a point. See the 4th column "side pix" here:
http://www.3sx.com/store/faq/99/index.asp
If you wanted to combine the 1G Fiberglass 99 bumper and the RT corner/snake lights, you'd have to have your body shop modify the bumper to mate with the lights, but looking at it, looks like they could just lop off the top outer portion where the turn signal goes and fit in the 1G RT corner/snake light assembly.
Hope this rambling helps!?
EricB