I would pull out the Cam Position synchro, in the old distributor hole, that drives the oil pump, synchro shaft could have snapped.
Get a drill with correct extension and tip to turn oil pump shaft.
Turn on key and see if you can get oil pressure using the drill.
Don't remember if is goes clockwise or counter-clockwise, try both ways, won't hurt any thing.
But because of the "thud" you may have lost a bearing or seal, and that lets the oil flow out of that passage too fast and you lose pressure in the rest of the system.
Oil pressure is Back Pressure.
The oil pump pushes out too much oil for the system to use, even at idle, so a back pressure builds up, thats oil pressure.
If a passage opens up, well it's like putting a big hole in a soaker hose, nothing makes it past that hole, goes down to a trickle farther down the line.
Possibility that the oil pumps pressure relief valve blew off, that would make a noise, or even the oil filters relief valve.
Is the oil filter still there, no holes in it?