Hi and welcome to the lunatic fringe
. '73 eh? A bit of a changeover year for VW's. Different trans mounts started in that year so it may pay to check what sort of gearbox mounts you've got. Well, if the engine's out (or coming out) you'll have your answer soon enough!.
Balancing....grey area. I believe the flex plate is zero balanced as a standalone, or as part of the crank assembly. I say this because of the 3 I've run across they have all had a small series of holes (varying amounts)in them and the motors were never rebuilt. I lean more toward standalone balance as no manual I've read mentions re-assembly in the exact sequence they were attached. I'll check over my spare converter for balance weights but seriously it would need some very specialised equipment to do it and no other converter I've seen has balance weights on it. Just think of how much damping a TC full of ATF provides!!!
Since you are rebuilding you could get it ALL balanced in whatever flavour you want, but then you *would* have to mark re-assembly points. This can be negated by zeroing the flexplate and TC and then just sorting the crank and attached parts balancing. I would have a serious chat with your engine rebuilder about the whole balancing deal.
Far easier on a manual because you've got about 15 1/2 Lbs of metal to remove material from hanging off your crank, and I would pay attention to the remove/assembly sequence ALL the time.
Getting the flexplate off? Big 3/4" rattle gun and appropriate socket is the quick way. Another less painful way than what others have tried is to bring No 1 piston up on the compression stroke then wind in some 1/4 or 3/8 rope into the plug hole (leave some hanging out..) then armed with suitable socket (36mm) and breaker bars/pipes undo the gland nut while the engine "self locks" itself on the rope. Have a mate helping you hold it all down as you wrestle with that 250 ft/Lb torqued sucker!!
Once you've got it off (or fished your mate from the other side of fence
) wind in two 8mm bolts (I'll check the size for you) that have been nicely "face flattened" (for the cranks sake) and they will get the flex plate off the crank. You could maybe just pop some small washers down there too. It could also just pop off, but you never know....
The TC bush....nasty. A UK member here (AutomaticSamba) is (was?) in the exact same predicament. They appear to have been discontinued/NLA. You may wind up having to get one made.