Adjusting valves on a 65 273?
I adjust my valves with the engine off and cold one cylinder at a time. I adjust them cold because I don't like burning my fingers and not running because I couldn't keep a socket or wrench on the rocker. I pull the plugs so the engine is easier to pull over with the fan blade or a socket on the front. You can pull the distributor cap and watch the rotor to get an idea of which cylinder is at top dead center on compression stroke. Firing order 1-8-4-3-6-5-7-2.
The clearance will tigten up when the engine runs and gets hot, a little tight won't hurt. This has worked for me for 45 years with good results.
Try the different suggestions and see which way you like best.
Isky recomends adding .002 to the adjustment when adjusting cold to get the proper hot lash.