If you have the electric starter installed, turning the motor over backwards is difficult. Remove the spark plugs so the engine turns fairly easily.
Don't turn over the engine using the large "nut" on the points shaft: this is a fragile piece - it's easy to break it this way. Remove the alternator cover and turn the engine using the head of the centre bolt. If that comes loose, you can just grab the alternator rotor and turn it.
The marks are visible through a hole in the points plate, T 1-4 and T 2-3 (TDC for 1&4, TDC for 2&3). It is not critical to be exactly at TDC, just close is OK for valve adjustment "my way".
I do the valve adjustment in four steps. You can do it in two but that is confusing to me, I like to do one cylinder at a time rather than jumping all around.
Turn the engine to T 1-4. 1 and 4 will both be at TDC - one of them will be between compression and power stroke and the other between exhaust and intake strokes... but which is which?
My easiest way to find compression stroke is to watch/feel the intake valve tappet: it closes (the tappet end of the rocker rises) as the piston reaches BDC before going up on the compression stroke.
I get #1 at TDC after compression stroke. Both #1 valves will be fully closed, and I adjust both tappet clearances.
The firing order is 1-2-4-3 so next I rotate the crank half a turn to T 2-3: that will have #2 at TDC after compression and ready for tappet adjustment.
Another half turn to T 1-4 will have #4 ready to adjust.
One more half turn to T 2-3 and adjust #3.
Done! I just go around again and check them to be sure: feeler gauge with nice drag and the nut tight.
If any tappet clearance is super tight after loosening it a turn or two, you are probably on the wrong stroke and the valve is actually slightly open.
