for oil to move up through the pushrod the engine has to be running. there's a metering disc in the lifter which normally locks in oil, as in hydraulic lock because it's a hydraulic lifter. as the lifter comes down off the cam lobe, the oil should shoot up through the pushrod to the head. i believe you'll need all lifters in and pushrods in with rockers tightened down and correct preload on the lifters, then crank engine via starter with ignition disabled. you should see some oil make it to the head. if you have one lifter out you'll have no oil pressure in the lifter galley and not get oil pressure to allow oil to make it up the pushrod. Other than that, only other thing I can think of is cam bearings might not be lined up 100% and you're not sufficient oil to the lifters, or you have the wrongs lifters and the oil hole in the lifter is not lining up with the hole in the lifter bore so oil isn't making it properly into the lifter.
But just with all lifters in run your oil priming tool and oil should ooze up around the lifters and you should measure at least 30-40 psi on a mechanical pressure gauge. If that happens then you should be good to go. crank the engine, idle it for a couple seconds with rocker cover off and you should see oil. hope that helps.