As I understand it all Omega B/B2 use 110mm arms excepting the later BMW 2.5 diesels which were not sold in the UK.
The ZF catalogue says the 121mm parts you bought are for 'extended wheelbase' variants, so they're for Omega A/Carlton limousine models, not the standard models. Not many of those still around and nothing to do with the absence of power steering.
EPC 2001 says 90092492 is for Carltons with C20NE, C24NE, 18NV, 18SEH, 18SV, E18NVR, S18NV, 20SE, 30NE, C30NE, LOTUS, 23DTR, 23YD and 23YDT - All WITH Power steering. About the only Carlton it is NOT for is the C30SE/GSI3000.
So the part Andy A has bought fits/fitted the majority of cars. It probably fits the majority of Carltons still on the road (Lotus!). Famous last words though - never heard of one failing on a Carlton.