Realistically, it's easier to take it to Circuit City, Best Buy or wherever you get your new speakers and let them install it. Most of them have either free installation or minimal install charges. Not only do they have the specialized tools to remove the interior door panels, handles, etc., if they screw it up they're responsible for fixing it at no extra cost to you.
However, if YOU screw it up or damage something else in the process, the only person you can turn to and blame is the one in the mirror.
in the front doors their 6 1/2 in the back for a pickup their 4x10
Stock speakers should be 4x6's
the size of the speakers are 6.5" round
6.5" front and rear door speakers
If they are stock then there electric.
4X10's
All the speakers in a 1991 Chevy Silverado should be 4x6 if they are stock.
Probably a turbo 350.
6.5S 6.5S
3-1/2"
Generally, a stock silverado will have four speakers; two in the dashboard and two behind the seat.
I have 4" in the bottom of the dash in my 90 model, 92 should be the same