did some research on T rex before I wrote the scene, and I'll answer your questions based on what I learned.
Would the T rex be able to feel the difference of the material of the shorts on It`s tongue, and feel and taste the guys maleness and genitals throu the material?
Probably not. For the T rex the average adult male is literally one bite. The genitals would be no more than a crumb in its mouth.
Would the T rex enjoy the feel and texture and shape of the guys large shorts wrapped manhood etc?
The shorts might actually be annoying to the dinisaur as it swallowed because they would impart a rougher texture and perhaps dry its mouth as they soaked up saliva.
Once it had finished eating they guy how long before digestion would start.?
It would begin almost immediately.
How long would the large meat in the shorts last in the T rex`s stomach ?
A few hours. One adult human wouldn't even be a complete meal to a T rex and would be digested very quickly.
What about the shorts ,what would happen to them in the stomach of the T rex.
They look like synthetic material, so wouldn't digest. The stomach acids would fade them, but they'd probably remain in one piece.
would the Aztecs find any remains or traces of the guy in the dino poop?
Only the faded shorts. T rex was able to crush bones and digest them completely. There would be nothing identifiable left.