L jetronic (old school) AFM compatability?

[e28 man]

I have a 1980 grey market 635. I need an AFM (pretty sure on this one) and can't find one. Ralph in SoCal off bigcoupe.com has one off of a 1981 US 633. Its still L jet but his car has the 122 ecu. I tried putting one of those in my car and it barely ran. he said the AFM is usually matched to the computer, thus meaning his wouldn't work with mine. Anyone know L jet well enough to tell me if this is true?

[Bentsdl]

Maybe this can be of some use:
http://www.firstfives.org/faq/ljet/bosch.html
I think you are looking for a 0.280.203.002 AFM. As far as I know you can't interchange AFM's with different numbers. But a 0.280.203.002 from a 77 633 worked also in my 79 635. So as long as the number is right, you should be okay.