No, you cannot swap ECU's between Fed and Cal Vanagons:

California Models:
071-906-021B All Transmissions 1980-1983

Federal Models:
039-906-021E Manual Trans 1980-1983
039-906-021C Automatic 1980-1983

Only Vanagon ECU's will work in a Vanagon.

The ONLY aircooled ECU in all the Fresno and Madera self-serve yards is a Fed manual one in Westside Auto Dismantling. The one in Pick n Pull is a melted glob...... I have been looking for a Calif ECU for over a month. It seems like all the Vanagons showing up are wasserboxers. Pick a Part in Fresno just put out a complete 84. Pick a Part in Madera has a later, Wolfsberg edition Vanagon

Not sure why Bus Boys says the 80-83 manual ECU is the same as the 79 Cal auto ECU.

The 79 Cal auto trans ECU Bosch short number is C105X.
The 79 Cal manual trans ECU Bosch short number is C104X.
That is all these C numbers fit.

A while back someone asked what the difference was between all the ECU's on bay window buses. VW/Bosch made 4 per year model. Cal auto and Cal manual, Fed auto and Fed manual. I said I have never felt a diference in any of them when I test them in my 77 Westy. With that in mind, I just went to my EKTA disc to see what VW says the part number of the ECU should be.

That 039-906-021B that Bus Boys says fits fits 79 Cal manual trans.... well EKTA says it is the ONLY ECU available for ALL transmissions in these applications:

1) Calif, from the start of the 77 year model to the end of the 78 year model
2) ALL Fed bay buses from 77 to the end of 79. EKTA does not show it for 79 Cal!
3) ALL aircooled Fed Vanagons, 80 to 83.5.

The Calif Vanagon is 071-906-021B

No wonder I never felt a difference! There isn't one.