Was not sure what electrical section/audio section to post in so I am taking a shot here. If it needs to be moved let me know please.

Basically as I make the chassis ready for a motor swap and continue to drive the vehicle daily I need to upgrade the audio system in the truck. 1990 ext cab pickup with the 3.slo.

With that said plans are as follow:

Create a lift block to put under the seats or brackets to raise the seat in order to mount the amps underneath. Looking to make a custom box out of most compartments. The 2 rear panels that have the storage will be turned into where the mids go. Most likely 6-8" in each. Plan on adding 2 or 4 6"/9" coaxles on the bottom of the storage panel under the rear seats. Mount a shallow sub in the larger of the 2 storage units on the bottom if i still feel the need but going to wait until I have the mids in there. Also add 2 highs into the front pillars. Want to use a single din unless i find a great deal on a double din. Also looking into door speakers and making and putting the 6"/9" set up front and only doing 2 in the rear. I am not sure yet. I am going for quality over sound. I absolutely hate static.

With all that said here is my question. Can i fit larger than a 4" speaker in the dash? I have not opened it up. How large is the inner part behind that screen? How much plastic can i cut away before i cannot mount anything?

Thanks in advance.

 

4" in my experience is about it. A 5 1/4 won't work. Those dash spkrs mount right under your vent, and the hose touches the back of those 4". I picked up some 4" eclipse awhile back and they sound great. I ran 2 multi directional dome tweets on my front pillar, 2 directional tweets on the mid pillar, 2 nakamichi 5 1/4's in the rear doors, and behind the seats in the panel about where the back seat folds down, a 10" on each side, then between the 10's but forward of the storage pockets, I mounted 2 5 1/4 Rockford fosgates. And the 10's are a bit shallow, aka smaller magnet. I enclosed these building an internal "box" after watching a YouTube video on making your own using fiberglass resin and fleece material. Beware the subs, I've found I have to lower my back window to get better sound as my truck is pretty airtight. My amps are mounted under each front seat, no lift blocks needed. I run a 1000w 2 ch, and an 800w 4 ch.

 

You can fit 4x6s too. But I'd recommend getting the factory SR5 speaker boxes in the front and using weatherstripping between yoru speaker and box to really get the speakers to pop. For the boxes, they're designed for the 4" Toyota speakers with just two screws so you have to shave off some of the support bars. On the drivers side, I used washers to give my speaker with a larger magnet space (4" alpine, really like them). And then I also had to use a couple washers between the drivers side lower dash panel and the frame -- on the lower bolt connection. Others have cut out the speaker box and used dynamat, but I think my way is easier and gives enough space...

 

Most Toyotas had used these crappy 4T speakers....and on most of them there isn't enough room to put bigger speakers in, and when you do they still don't sound right. Keep in mind the dash speakers are playing music to your knee caps

Thankfully, aftermarket 4" speakers have been getting better over the years

 

4" is all I could see fitting, maybe a 4x6 plate speaker with some work. I use Boston Acoustics S45 speakers - sound great to me. I strongly doubt you will "need" more than 4speakers and a sub in the little cab. Another option is use the dash speakers for CB radio and add door speakers(components) for your fronts instead.