[Arran]

I'm having a difficult time removing the solder from the old sockets.  I'm not the first or even second to rework this chassis and the sockets are loaded.  The heat required is cooking the socket material.

 Try a solder sucker, one of those types with a spring loaded plunger works well, or one with the rubber bulb. With the rubber bulb ones the hole in the tip is often too small so it sometimes helps if you drill it out large enough to accept a finishing nail, after which the nail can be used to remove blockages. Sometimes it helps to ad a small dab of fresh solder to the tip of the iron or gun whilst trying to heat up and remove the old solder as well. Another thing that is useful for removing solder is a flat bladed jeweler's screwdriver, one of the medium sized ones like you would use to loosten the set screw on a knob, that you can use to push the molten lead off the terminal.
Regards
Arran