I picked up a 51J4 (3 filters, good SSB/AGC mods in place, 4:1 tuning, 1/2 KHz end to end on the PTO -- how could I complain!) that works really well. Didn't notice until I'd been staring at it for a while that the meter is a replacement -- with an "S" meter scale and a 0-400ma current scale. Probably from some unknown Collins transceiver (?). The meter bezel is also a very good black, rather than the usual reddish (in the light) tint. The S-meter scale is quite accurate. I haven't put a cal'd generator on it yet, but it matches my K3 readings on comparable signals quite well.
I thought I might look for an original replacement, but I think I'll just leave this one in there. Wonder if anyone recognizes the source?