I do want to jump in here a little.

The SIIA and SIIB F/C share a lot if not most parts with the normal control SIIA Land Rovers.

The ENV axle assemblies are orphans, but the last production SIIB had Salisbury front and rear and the swivel assemblies are the same parts later used in SIII.

The firewall is a modified 4cyl one, only slightly changed by a hole in the floor for the steering column and some rivnuts for the front panels. Doortops, windscreen, truck cab roof are the same parts. The seatbox, door bottoms and transom panel are modified from the normal control versions. Dash panel and electrical are essentially the same but with different ratio speedo, even the fuel tank are based upon the same design as the 16gal station wagon tank but filler moved to the rear.

Gearbox and transfer box case and gearbox gearset (excluding mainshaft) are the same as the SIIA versions. the transfer box gearset are orphans.

Engines apart from the water pump on the 6cyl are the same. Front springs (and rear on the SIIA) are interchangeable with the normal control versions, particularly the Au Military.

If you are keen you could make a SIIa forward control by sitting the F/C upper chassis on top of an SIII I ton or Au military chassis. This is why the SADF were delivered SIIB F/C during SIII definitely as late as 1974, because most of the required components were still in production in the U.K.

My SADF SIIB radio relay entered service in 1977, although the rolling chassis was likely built in mid 1974.