Mostly what was in mind when I made the above posts were the after market ECU systems you can buy. I know it's not exactly the same - but I'm hoping that someday someone will make a aftermarket ECU for electric cars.
Superfastmatt on YT put a 50s jag on a tesla drivetrain. But, IIRC, he took care not to mix-n-match, in order to sidestep integration work.
Obviously an electric vehicle doesn't have fuel injection, so s/ecu/motor controller/g. But I understand what you mean.