There are two different sizes of disc brake set ups, OHV have the small (8 inch) discs, and OHC have larger (10 inch) disks. The mounting lugs for the caliper are the same across the range. The stub axle is different on the OHC disk brakes, the mounting lugs for the caliper are further out from the center to accommodate the larger disks. Lockheed and Girling calipers are interchangeable, ( i.e. they both use the same mounting holes), but as you say, fit a pair.
Dunno about 'G14', but as far as I know, there are 2 sizes of girling calipers of this type , M16 and P16. M16 are the ones Ford use and P16 are the vauxhall ones. Some triumphs use the P16s too. The ford ones wont fit, but look identical.
Of course I may be wrong, but this is how i remember it to be. I've not really had much to do with disk brakes lately