Against my better judgement, I obtained a DEC SRC Firefly dual processor card. If i read this* correctly, then this card is interfaced to the shared memory bus (MBUS) as opposed to the QBUS (the card uses a Q bus format).
I realize it's probably hopeless, but I'll ask anyway: Are there any schematics or specifications on the connectors anywhere? *IEEE Computer, also available on Bitsavers as a technical report.