Sorry to hear of the fire, glad you saved it.  A few things to check:
1) To make sure the large wire system is working: jumper the starter solenoid to see if the starter turns over (make sure car is in park with emergency brake on).
2) When you replaced the wiring going to the auto transmission, any chance a couple of the 4 wires got interchanged?  With the melted insulation, it is hard to see wire colors.  There should be two red - light blue wires going to the transmission neutral switch for the starter interlock.  The other two wires are for the back up lights, do they work?  If the fire got far enough down, the transmission switch may have been damaged also.
3) You mentioned checking the fuses.  There are also fusible links that need a meter to check unless they are totally fried (visible).  Since you have lights, I suspect the fusible link needed for the starter circuit is okay.

I can scan and email you wiring diagrams for the 1971 starter circuit.  Scanned diagrams do not show up readable here do to picture size restrictions.  If interested, pm your email address and I will send them.  I have two 1971 diagrams, one dated 8-1-70 and the other dated 4-30-71.  Not sure what the difference is but can email both.