The new glow plug relays are nice, they leave the plugs on after start up which makes it much nicer in the winter. Here are a couple other things that come to mind:

Injector Return line replacement if needed.
Diesel purge to clean the injectors.
How's your clock and tach? those are fairly simple fixes
Shocks? I put bilstien's in, put it back to original ride
Clean the banjo bolt? if dirty this will give you a huge gain in performance
How are your axles? no rips in the boots right
Rear differential fluid change?

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1983 300TD - 202k with 5 speed Getrag conversion