I'm fairly certain that all 90 - 93 ECUs should be interchangable. Am I right?

Asking because I want to go megasquirt in the coming couple of months and I figure having a spare ECU to wire it into would be nice, so it can be done while I am still driving the car.

90 - 93 ECUs, inetrchangable or not?

 

To the best of my knowledge, all 90-93's are the same, except the 93 california ECU.