A: Timing marks have changed during time. While most dampers have the mark 10 degrees BTDC (with a timing mark the same way, so it equals out, but you can see the mark past the water pump better) they came with 2°, 8° and 10° over the years (but I'm not sure about the years and exact numbers, just know they changed, could look it up somewhere).
B: The balancer can slip, but that doesn't happen often
C: The engine should be advanced 6°-8° static. That is if you turn over the engine slowly (i.e. with the starter and only clinder no1 spark plug connected so you get the flash, but the engine won't run) you should get those marks. The engine needs more advance than that at idle to run properly, that's what the vacuum advance is for. At idle it will need as much as 20 degrees MORE than the static setting. My engine doesn't idle at all at the static setting, it simply stops. Because the engine doesn't run at this setting, you can leave all spark plugs connected and just disconnect the vac advance. Then have someone bump the starter for you and set the timing (also called initial timing) to 6-8 degrees. Then reconnect the vac line and you should be ready to go.
BUT: Very many people don't do it like this, they set the engine by tach or by ear. If you have one specific throttle setting, then the highest speed achievable by turning the dizzy without getting detonation is the most economical and efficient setting. So connect everything up (also the vac line) and set it to the desired speed. If you should find out that the engine speed at idle is then too high, turn back the throttle stop screw and reset the dizzy. Do this until you get the right idle speed and this is at the best dizzy setting. Then you're done, if you don't want to go further and bother with adjustable vac cans, springs and weights. Then it gets difficult, but this should get you in the ball park.
Hope I could help...
Mad