When I had my 91, I didn't really think it was worth it to replace the 3 1/2" speaker in the dash. I'm not sure about the older ones, but the 91's had openings in the doors for 6 1/2" speakers, so I just spliced some wire in at the dash and ran it through the door and put the bigger ones in. I know that wasn't what you were asking for, but if you can't figure out how to put the dash ones in, this might be another option.
-Dubbs