[Arran]

Is there any chance of obtaining replacement umbilical plugs? Somebody (not me) broke these. Probably prying them out of their sockets with a screwdriver.

There may be source for similar plugs elsewhere but I wouldn't count on finding them as they were likely proprietory to the Philco 690s and maybe only the 38-690s. Most of the two chassis sets I have seen use a 7 pin plugs and sockets to tie the cable to the chassis. I would take the plug apart and try gluing and filling the wafer back together with two part epoxy, preferably high heat epoxy without metal fill in it (do not use metal filled JB Weld) you may have to clean the phenolic material up good before you do. If it's really bad you may have to make a duplicate of the original wafer and replace it altogether.
Regards
Arran