Hi Chuck,
If you have been fortunate enough to track down a vertical sided sump of OT1600 appearance similarity, then the attached image shows one solution commercially marketed to providing sufficient sump depth by use of a machined spacer matching sump/block flange layouts and longer bolts/twin gaskets, and/or use of shallower Fiat oil pumps.
One local solution to larger twin cams motors in rear of 850 chassis has been to use Fiat Regata tin winged sumps (alloy versions available) in the interests of sump road clearance. Not for replicas as authentic as possible, though, as the wings require some adjustments to muffler locations to clear.