Ok, I did mine last weekend, I'll give a quick walkthrough on the order I took things out of the car. If you can find the TSRM here for the 90 Supra, look under the Body chapter at the Safety Pad, that is the dash components (not including the heater). If I can figure out how to post pics, I'll put up the pics of what it looks like without the dash.
Here is the order I removed things:
1 Drivers seat
2 Instrument Center Cluster Finish Panel w/ ashtray (covers radio & climate controls)
3 Console Box (between seats)
4 Shifter
5 Instrument Panel #1 under cover (under steering wheel)
6 LH and RH Cowl Trim (kick panels on left & right)
7 Instrument Lower finish panel (has switches for Fog lights etc.)
8 Unbolt the Steering Column from the brace behind the dash (2 14mm nuts on either side of wheel just behind ignition )
9 Instrument Cluster Finish Panel
10 Radio
11 Heater / AC Control
12 Instrument Guage Cluster (unclip the speedo cable from the dash)
13 Instrument panel #2 under cover (beneath glove box)
14 Glove compartment door
15 Glove compartment panel (interior of glove compartment)
16 ECU
At this point, mark what connectors should be coming out where (take pictures if you can)
The next item to come out is the dash itself. There is a nut or two at the back of the dash behind the guages way in the back. There are also some plastic guide pins in the edge of the dash under the windshield that pop into place so be careful pulling out the dash, just pull straight foreward. If you angle it when trying to remove it they may break. Also be on the lookout for some electrical connectors on the passenger side for some sensors and such (temp sensors for the heat/ac system, both above the glove compartment).
Once the dash is out, note where the wiring harness runs (again, take pics if you can) as it must be moved to remove the brace in front of the heater box.
The heater box is the one on the left, but you need to loosen the center section to be able to slide it out (careful, it is the AC so don't pull too hard on it). Once it is out, pull the heater core out of the top (I had to remove most of the screws holding it in) or you can change the pipes coming out without removing it (there are some o-rings that seal the pipes to the core).
When reassembling, the biggest thing is getting the wiring harness back in place and making sure to get everything hooked up. I messed up and didn't hook up the connection to the heater box and had to climb under the dash once it was reassembled to hook it up.
Overall, I spent about 1 1/2 to 2 hours getting the dash out, another 1/2 hour playing with the heater core and another 2 hours on reassembly. Again, take picture if possible, thats how I figured out I didn't hook up the electrical to the heater box as I couldn't remember doing anything with some connectors.
Hope this helps.
