I think we're too early for the Hercules to have the aircraft in service before WW2. Though the Hercules engine was first run in 1936 so the pre-war aircraft could be "designed-for-but-not-with" the Hercules. Settle for a smaller engine until the Hercules is ready.
I'd stay away from the dual role combo DB with torpedoes, instead we're looking for an early British Val or SBD. No one is dive bombing with a Mosquito, but a CV-capable, folding wing twin DB could be doable. It will need to be narrow to fit down the 22ft wide lifts. But has there been any twin DB capable of near 90 degree dives like we're looking for here?