I know that this has been an ongoing topic for the CCA but I don't remember if anyone has published the measurements of the original tube sockets.  I found these steatite sockets along with a bunch of surplus parts and wonder if they will directly replace the original octal sockets in the 516F-2 without the need to modify the holes with a file?

Center to center mounting hole spacing is 1.5 inches, mounting hole diameter is 0.146 inch which is a clearance hole for a #6 screw.  The steatite socket diameter will fit through a 1.063 inch hole (1 - 1/16") with some wiggle room. 

These sockets are WW2 vintage, salvaged from pre-wired tube socket assemblies that were never installed in a chassis.  The resistor values predate the current RMA standard values.  The quality workmanship standards were obviously not in effect early in WW2 since several tube socket terminals had wraps of wire stubs under the solder, the obvious result of wiring errors.

The upper groups of resistors are in tolerance, the lower groups are not.   As expected, the majority of 500 ohm cathode resistors are still within 10% while the majority of the 250k plate resistors are not.  If there is any interest, I can measure the domino style capacitors to see how well they have held up over the 85 years since they were soldered to the tube socket pins.

No end in sight for the hot summer weather here in Arkansas,

Jim