Looks almost as bad as my '62 /6! The deposits are from crappy oil (old Quaker State and Pennzoil that used PA crude oil bases in the 60's and 70's was well known for a lot of this type of crudding up), and perhaps limited oil and filter changes, and a lot of short in-town driving. The carb may also have been leaking after shut off and gotten gas into the crankcase and oil repeatedly.
This is a good indication that your valve guides have crud/varnish in them; this will cause sticking valves (/6's have low valve spring pressures so the valves stick easily), poor running, and misses. Since the car will idle, start it up with the valve cover off. The oil won't do any thing but dribble off of the rockers. Look at the rockers from the front of the engine and study the closing motion on each one. If one or more of them looks 'lazy' when closing, you have gunk in the guides.
To clean the guides, use the rope trick to hold the valves closed and remove the valve springs on the cylinders, one cylinder at a time. (Ask if you don't know the rope trick....) Work some carb gum cutter down each guide work them up and down 'till they are free. Put in new valve stem seals while you are at it.
This won't solve any carb or ignition related issues but may cure your misses. And setting the valve lash won't be reliable and consistent with sticky valves. This is just something I would do due to the gunk on the inside.
I would also not try to clean this crud out in any fast way. There is just too much and you may end up with a pan full of crud, blocking up the oil pickup from time to time. BTDT! Just use some good detergent motor oils for a while and change it and the filter a lot for a while.
I also suspect your timing chain is well worn with this kind of oil abuse. Another good long term project.
Set you timing at +5 BTDC or so as a starting point, not 0.
The suggestions on the carb idle circuit may well be spot on. Have you checked the float level while running (wet float level)? Remove the economizer valve (the thing on the bolw with the triangular cover), and idle the car level. The fuel level should be 11/16" below the flat top of the hole that the economizer valve came out of.
Your poor running symptoms after the choke drops off may have something to do with the ignition coil, points, or ballast; a weak ignition can do this, although it should just bog and have a very poor idle,not quit entirely. The points gap should be at about .017-.018". The ballast should be about 0.6-0.8 ohms cold. These are easy things to check.
Have you done the compression testing yet? And have you actually measured vacuum while idling? In other words, how do you know you don't have a vacuum leak?
