UDC= Upper Dead Center...........now called TDC= Top Dead Center. The 10 is ten, 10 degress BTDC (Before Top Dead Center). There is a 1 near UDC, that is TDC dead nuts. Between 1 and 10 is 5 deg BTDC. "Before" is advanced timing. The spec for sea level and the octane used in 1966 is to set timing at the 5. Your motor may run better at 7 or 10 or whatever, All that is later when timed with a light.
Right now you are trying to confirm that rotor and dizzy wires are correct. There are two TDC's, one is an exhaust stroke. One is a compression stroke. Both will show the timing mark at about TDC. One will not fire, the other will. That would be the compression stroke. If a person sets the dizzy up to the exhaust stroke the rotor will be 180 degrees off. If they wire the plug wires wrong, timing will be off in any number of ways.
So this is simple. You figure out when no.1 cylinder is near or at top on the compression stroke. You will feel the force if you plug the hole with thumb or finger and see the mark is at or near TDC "1" mark. Then look at rotor.
If you are at TDC on the exhaust stroke you won't feel any pressure. It's not super critical exactly where the pointer is. Should be at "1" or towards 10. It all depends on when a person stops turning motor when they feel pressure. You can then bring crankshaft around twice and stop at 5 BTDC, then look at rotor again. It will fire and probably start if anywhere near. The fine timing later is to get it running good. Right now we just want to hear a few pops.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
