Ok, you just need to check how to the IRQ is connected to the 68020 and make sure the driver provides the vector from the DUSCC. It looks like many interrupts can be polled in one go through the 74ALS240 on page 17, question is where the IRQ is routed and if it in fact interrupts the 68020 CPU at all, I may be that it causes a generic interrupt for the 68030 which reads the interrupt source and deals with it, in which case there is no vector from the DUSCC.

Because I can