you have oil coming out of your oil filter when you turn starter so your oil is circulating.
If it's running ROUGH at idle, under 1000 RPMs, you oil light may come on because idle is too low and oil pump not working as hard.
Put it back together, turn it on, rev it while it's idling ROUGH and I bet your oil light will go off and your gauge will read some pressure....listen for any noises...if there ARE no noises, oil is circulating, which would mean that the cause is somewhere else, possibly in your fuel system.....
Just trying to help
@Dragonslave......
Let us know....
Crazy Marky