Nice, you got it already. Sounds like the last guy used the resistors to drop the speaker-level output from the head unit to the line-level the amps expect. When I first installed the head unit in my '95, I didn't do that, and two stages of amplification meant it got loud quick and didn't sound very good. It also meant that the stupid beeping noises from the Sony head unit were painfully loud.
I've got stock-size oval mids in mine, with the tweeters and high-pass filter caps built in. They were already (poorly) installed when I got the truck, and they were in good shape, but they didn't fit right and the last hack just sorta stuck them mostly in the hole and used longer screws. I guess the factory Clarions were a little slimmer than modern aftermarket mids. I'd run into the same problem on my '95 when I put Boss speakers in it, so I'd already trimmed a set of the plastic mount adapters, and I just swapped those in.
I've got nothing against rounds, I just used what I had. Most any aftermarket speakers should sound better than what's left of your factory ones at this point.
While I had my doors open, I stuck some sound deadener to the sheet metal and made blockoff plates to screw over the holes in the inner door. Sealing up the door cavity like a speaker cabinet is supposed to improve the bass. It doesn't make it sound like it's got a subwoofer, but I think it helped.