Well, 1990-1991 Pros has dash provisions for speakers, in 92-94, they took away the grilles on the dash panels. But since mine is a 90, and i wanted a 3 way comp set up front, i was good to go....(i know, they are not at the best angle...but i'm working with what i got ) i did this a LONG time ago with a set of Infinity Kappas, but i just mounted them in the metal brace that was there. but when i got the new DEI speakers (still a while ago) i wanted a better mounting location. I used a peice of ABS plastic and begun to shape it to fit. I left the brace as is, since i already had a hole cut for a 4" mid. I made it wrap around the corner for 2 reasons...1) it would mount more solidly and 2) creats a baffle and seals the front and rear of the speaker better...

anyway, after a bit i came up with this.
(this is a very old pic, maybe 2 years, so most everything else has changed as well)