340 Oil Priming Question First Start

I'll also add that I have always looked for the location where oil shoots up to the shaft. Keep the oil pump turning at that location and you should see oil exiting each rocker somewhere even if not so much at the top.

BTW, what rockers are you running? Are they 273 adjustable rockers with a flat tappet cam? I remember running a 273 with the valve covers off in an attempt to adjust valve lash while running. Not good. Oil got everywhere and made a mess. : )