I have a 94 YJ and are the dash speakers 4"x6".
If you're thinking of doing an upgrade to your speakers, and you're pulling your dash out, you could also switch to 5 1/4" speakers. I don't know a whole lot about the physics of car audio, but the idea is that oval shapes aren't as good/efficient at producing pr pushing sound waves as circle shapes are. So, replace 4x6 with 5 1/4 and replace 6x9 with 6 1/2 when you can.
eBay has some brackets if you're wanting to go this route while you have your dash apart:
4x6" to 5 25" Jeep Front Dash Aftermarket Speaker Adapter Bracket Spacer Plate | eBay
How is it setup? Through the head unit, or with an amp? With an enclosure, or in the open?Would you run a 4x6 for bass, or for clarity?