How much are u looking to spend? And what are u expectations? Are u using a factory radio or aftermarket headunit?
I have a Custom model and still had speakers in the doors, although mine is an 88 model with no dash speaker. I also added two 6x9s in boxes behind the seat (mainly when i go out the bush parties, heh).
If u want to keep it looking fairly factory u should be able to put a set of 6 1/2" speakers in the doors in the factory location and use 92+ rear cab trim to get a set of 6x8 speakers in the rear cab corners.
Just remember, one good set of speakers will be better than several sets of lower quality speakers. And u really dont need more than 2 pair in a vehicle, especially a regular cab truck.