~~First Summer out of H.S., '88, I worked for Ming's Auto Beauty which detailed used cars local dealers newly acquired. One day the 2nd Pontiac to ever appeal to me came in, first being '64 Tempest. I was in a bit of awe to register the year&guessing '85-'88 Red Trans Am. GTA? Refer to it as a Crossfire due to the placement the dual carbs found under the hood. Hit about 18 MPH in gear w/o giving it gas. It's the only one I've ever seen despite the number of times I attempted a search?

~~Was this a special/limited production model? Or did somebody personally modify it? If so, they did a helluva job because it looked original/factory.

The Crossfire injected SBC was only used on the the 1984 Corvette, it was replaced by the Tuned  Port V8 afterwards. It  was a one year only deal for the Crossfire.

The Corvette used a 350 SBC, so did the Trans Am GTA. A regular 3rd gen Trans Am was only allowed a 305 SBC. I suspect what you saw was either an engine swap or an intake swap from an 84 Corvette.

It can't have been a 1985-88 T/A, as the Crossfire injection set-up was only used on the 1982-84 T/A's, it didn't last very long as it received a lot of negative feedback.