I think almost any double-DIN head unit will fit just fine without any modifications. If your head unit comes with an optional bezel, which many do, you just won't use it. You may want to look for units that have programmable button color schemes if you want to match the factory Supra green. (edited to add: or if you're mostly a full touchscreen with few buttons, you may want one that lets you upload your own custom background image)^^^ you also seem to know what your talking about...hopefully flightz71 will chime in here and give some more input...
I know there has to be a way to do this...these things are so advanced that i dont believe that there isnt a way to program this..
Anyone else have any info on this subject please let us know...this is killing me and its is the only thing holding me back from buying this head unit, but to me its a very big deal...i dont want to be driving an RC car around town
Many of the Kenwood units also have separate control wires for the amp turn-on and the power antenna control. If you want to be certain, you can go to the Kenwood website and download the complete manuals for their systems. I suspect other vendors may also allow you to download their manuals before purchase. It's a good idea to try to read the manual if possible before purchase anyway.
The speakers may be the most problematic if you're not wanting to make changes. Crutchfield should be able to help you, but do notice the difference when they say "fits" versus "fits with modification". Generally it is the screw-hole pattern that may not match; there seems to be speakers with 3-holes and some with 4-holes. You can make either fit with a bit of work, and look good, but getting the right one to start may be easier. In my '97, factory fronts are 3-hole while the factory rears are 4-hole. Also the wires to my rear speakers were soldered, but it is easy to crimp standard push blade-connectors on them. You can inspect the rear speakers easily by just popping off the grill cover; but you'll have to take the door panel off to get the the fronts as the grill covers are permanently attached to the door panel.
If you're replacing the subwoofer, some of them are just a bit deeper and will bottom out in the cavity, necessitating the use of spacers - which may interfere with the subwoofer cover. I understand that the tweeters are fairly hard to replace, so I just left them.
Also, the GPS antenna should work under the dash, though it may be ever so slightly less sensitive. Basically it just needs a clear line-of-sight to the sky - without any intervening metal. The windshield glass and thin plastic/foam of the dashboard surface won't block the signals, much. My Kenwood receiver is so sensitive it can even get a signal inside my garage, I guess through the side windows. Also, you can put the GPS antenna elsewhere too, like in the trunk area.