Alright, so I'm back at it again.
I can't for the life of me remember what I changed but I've got it idling fine around 7-800rpm 90% of the time. According to the tacho at least. I swear it sounds more like 12-1500rpm, but I guess I could be wrong.
Pretty sure all I did was block off a few vac lines, then unblock them one by one leaving EGR still blocked.
Manifold vacuum is around 18inHg (60kpa), and steady at idle, and the ported vac off the carby was around 6inHg (20kpa) on one side and (i think) 0 on the other one. Both ported sources rose at higher revs. Sounds about right? Pretty sure both ported sources should be 0 @idle. Seemed to run ok with the vac advance hooked up to the 6inHg plug (the original source for it)
If you give it a bit of a stab from idle it'll take a big gulp of air before revving, so something else in there needs to be setup better, and it still needs a squirt of
aerostart first thing in the morning, but with a bit more fiddling hopefully it will run well enough for the trip.
Found a little pool of coolant underneath this morning, and it looks like maybe the water pump seal has a leak, but there is also some dried coolant around the thermo housing. About 100mL of gearbox oil has leaked out since I filled it a month or so ago, and the new sump plug still leaks.
I think I'm adding more to the "to-do" list than I'm crossing off but it'll get there.