99 Ranger: can I put 6.5 speakers in the doors?
 

And will it be much trouble? I'm sure this has been covered, but I can't find it lol. Noob here.

Yep, you can. They sell 6x8 adapter plates.
or if your handy you could make your own out of HDPE or thin MDF board.

Depending how much xmax your speakers have and how thick the adapter is. you *might* have to wedge something between the plastic panel and the metal frame, to allow enough room for the speaker to move. I ran into this problem. I also had to trim a small thin bit of plastic behind the grill to have enough room. not really a big deal.

They'll fit with the adapters. Save yourself the money and just make your own adapters. You can go to Lowes and get a small piece of 1/8"(this is what I used to make mine) and cut a few pieces 6"x8". Measure out a 6.5" hole in the center of that piece of wood, drill a pilot hole(right term for that?) and take your jigsaw and cut it out. Screw the speaker into the piece of wood, screw the piece of wood to the factory speaker holes and be done with it. You might want to hit them with a light coat of black paint so you can't see the panels.

i didnt use adapters i just mounted them with 3 bolts pushed it all the way to one end and screwed it in and i wouldnt suggest mdf in the door like that cuz water moisture does get in there and they'll rot away pretty quickly

Thanks guys!

Hopefully you sealed off the large hole that was left. sealing off the immediate area around the speaker with a solid non resonate baffle is extremely important.
You will loose a large range of frequency response in mid-bass range (500hz down) if you don't
there will be a sonic hole in your system because the backwave of the speaker will cancel out the front wave in that range.

MDF is fine as long as you seal it with something paint, bedliner, polyurethane, etc...
HDPE is the stuff that plastic cutting boards are made of. you can find them almost anywhere.

adapters are only $10,
the best solution is which ever gives you the heaviest, stiffest, non-resonate most airtight results. (ive seen people use granite rock before, whatever works)

since were on the subject, Sealing off the rest of the doors openings with sheet metal and sounddampener will improve sound further. a closed cell foam mat behind the speaker will absorb the backwave, which will clean up the sound even more. Speakers in a tin can, sound like speakers in a tin can.