Gearbox numbers

I recently purchased a collection of gearbox parts. Included is this gearbox casing.
From my research I'm assuming its a series 3 Suffix D box as it has the ribs on the case.
However it has a Serial number on the selector/top plate S95103858. It also has "D" marked on it.
All the internals point to it being a D suffix box.
But, I am lead to believe that Series 3 gearboxes did not have this serial number on the top plate....instead it was on the transfer box. I think it is a matching case and top plate set due to the casting marks being the same.



Next, I have a transfer box with a serial number 90383337B. I am thinking this is a series 3 suffix B transfer box.

It has a date etched on the output shaft housing 29/6/78 and what looks like a "D" beneath.



Does anybody have any ideas on what exactly I have got here?

The gearbox casing is a later type casing . photo's of the gear engagement teeth would help should be cowboy coffin shape.
Suffix D box alkso had a different reverse selector shaft and the bolts holding the gate on its end are in the horizontal as opposed to vertical orientation.