To the best of my knowledge, neither the Cobra nor Merc A drive were used behind a diesel.
One reason being that the Dog Clutch gear engagement requires either the ESA or SI for gear disengagement.
I don't know how you would interrupt diesel engine RPM for Dog Teeth disengagement.
One method that will work, would be a Borg Warner bolt pattern flywheel cover for the 4.2l diesel, a Volvo Penta B/W (slash) V/P PDS adapter housing, and then use an AQ series Volvo Penta transom shield and Cone Clutch out drive.
The Borg Warner components will take you to the Volvo Penta AQ series drive with little to no modifications to any OEM parts.
The transom cut-out would require enlargement, of which would clean up any soft areas immediately around the Cobra cut-out.
No need for ESA or SI, and you would have a cone clutch drive (no more Dog Clutch).
It's also an easy upgrade to the Duo Prop lower unit.
