All the Oil passages are probably blocked up. You should have changed the Oil and Filter and added a little ATF to it to help clean it out.
The ATF acts like a Detergent that helps clean out the gunk. After it’s warmed up, drain the Oil and do another Oil / Filter Change. Use low viscosity oil or see if you can get some Engine Break In Oil.
Did you crank the engine with the Coil Disconnected to get the Oil pumped through the Engine?
Might just be worth the trouble to pull the engine and rebuild it. You will have to do it anyway if the Oil isn’t reaching the Top End.
Are the Engine and Transmission Numbers Matching? If not, put in a Crate Engine and new Transmission and turn it into a Resto Mod.
Or, just do what you want to do. LOL
Plugged up? Possible. Or excessive clearance any where can cause pressure to be inadequate. (including the pump or a stuck relief) Pressure is caused by resistance to flow. Its like washing your car with a big hole in the hose back at the faucet or somewhere else in the hose.
Plugged up is like when you get a kink in the hose, there would also be a lack of delivery.
Hell its been 25 years since I worked on a 383 other than maybe some tune-ups.