I pulled my cam sensor, poured a little oil in there, even though I did have the oil pump stuffed with vasoline, yes vasoline and it works and its only in there till I change the oil for the first time, which is after the initial startup. Used a primer, sbc primer from Jegs or Summit works just fine, spun it with my drill till I felt and heard the drill drag. Started right up with pressure!
Are you using a primer and a drill to prime?
You could always pull the oil pump feed line and fill with oil from there, so the oil goes straight into the pump, should help get the pump primed better for ya.