See if Pelican has some used pushrods for ya. Cams, lifters, push rods, and rockers all mate wear, but it's only critical on the cams and lifters. Without looking at them I'd guess they're O.K. for the time being, and I "THINK" you can put new ones in later with the motor in.
A "dropped seat" is one that has come loose from the head. It at least blocks the valve from sealing. At worst it jams the valve completely open so the piston hits it, somtimes this breaks the valve head off, holes the piston, jams the valve into the head, etc. A "burnt" valve is one that couldn't shed it's heat to the head (wasn't seating completely) so parts of the valve start to burn off. The valve looks like small "peices of pie" were cut out of it.
Sodium vavles can be re-ground, but like anything else it depends. If the vavle is past it's margin, if it is stretched, bent, cooked, or worn under size it can't be re-used. It is the luck of the draw. If they are fairly new and haven't be over heated you're in luck. You are ALLWAYS better with new sodium valves ($50-$60 a pop), IMHO good used sodium is next, then stainless steel. It all depends on how long you want the engine to last.
The valves being "sunk" like you describe is probably from a past valve job where the old seats were used, or it is valve recession from overheating is my best guess. Or it may just be normal, if they are all the same I wouldn't worry. Next thing is to clean the combustion chambers REALLY good and look for cracks. They usally form in the small area between valve seats or between the Exh valve seat and the spark plug hole. You can run an aircooled motor with cracks, but they will just get worse, and then the seats will drop.
Look at the tops of the pistons, should be dark (depending on mixture) and smooth. If it resembles a sponge, or there are little balls of aluminium on it you had a detonation problem. While the motors out you might consider seeing if any of the rings are broken. You will need a ring compressor and some assembly lube.
Can't remeber about the oil cooler coming off first or not. But it's so easy to do with the motor out (and fan housing off) why not do it now? When I take it off I soak it in a gallon of carb cleaner overnite to clean out all the fins. Don't submerge it though, DO NOT let the carb cleaner get INSIDE the cooler. The nuts on the cooler are a low torque (aren't all the 914 nuts
) so be careful.
Buy Tom Wilson's book on aircooled VW engines. It has all kinds of goodies to look for while the motor's apart.