Changing the whole truck to 12V is a right pain actually, engine is great, but then you also need to change out heaters, instrument bulbs, instruments in a lot of cases, wiper motors, etc. The 24V FFR is a nice system, so don't just dump it I say
If you did convert then a new loom would be the way I would do it, as FFRs tend to have pretty radically altered schematics... I really advise against it!
I don't know how good 24-> 12V droppers are WRT to noise on signal lines, but get a good enough one there should be no problem running the EFI system at all.
Keep the 24V starter motor, less amps in cold weather = more likely to start
EFI would be worth it for sure, otherwise wave bye bye to ~30-50BHP.