915 adapter should work, the bolt spacing is the same as the VW gearbox. if you haven't already done it, you shoudl just try bolting them up and see what happens. If they're just checking for quality of fit and security of fitting then you could probably leave the clutch and flywheel off and just use the adapter. Put a starter motor in the hole in the gearbox to avoid arousing suspicion...
best of luck
