A professor of mine who worked on the project as a PhD student once told us about the project:
According to him they had to use the heavily armored version of the car, intended to protect presidents, and strip out all the amour, because only this car platform could carry the enormous weight of the computers at the time.
Then it couldn‘t possibly have been in the 1980s. The 80486 didn‘t exist back then. The 80386 exists since the mid 80s but would have been very expensive.
The bus alternator produces up to 80 amps at 20 volts - while the computer needs 12, 5, and 3.3 volts, in the 1-20 amp range. Using a common inverter and a common power supply is the cheapest way to convert the voltage.
