I have nearly 20 Airfix 2Ds and I can make any aircon vehicle from them. If I need more, not hard work. My 2F FO is OK, but the fan is crude and I still have another box to lop off.
TSOs are rare but 2xBSO = TSO and BSO+FO=BFK
Bogieless specimins from Ebay are fine for this.
Those SP Roe Vac vents do not match Airfix either.
I think I will leave them OOB until I detail one.
As to Bachmann, they could add 2D 2E as well, what do we have?
2D TSO, FO, FK, BSO, BFK. 4 shells 2 underframes
2E TSO, FO, BSO. 4 shells, 2 underframes
2F TSO, FO, BSO. DBSO 4 shells, 2 underframes
Ignore roofs (use seperate vents)
TSOs 2D, 2E (early), 2E & 2F. 3 in total
FO 2D & 2E, 2F (I think, may be 2E & 2F) 2 in total FK uses same shell
BSO 2D & 2E, 2F. 2 in total
BFK, 1
DBSO - I leave this one to experts
So ignoring DBSO, we have 8 shells, 3 or 4 chassis (not sure on 2F BSO), 2 basic roof designs. To give us all Mark 2 aircon stock.
Using seperate mouldings down to one chassis and 3 or 4 fan units.
Would not be difficult for a manufacturer to produce the lot.