[David J]

Tube is not factory .
Make sure the fitting at the top of it is not screwed in too far .
If it is it will act as a dam and cause a major leak .
I have found 5 turns in is safe .
Also make sure the tube is clear .
I would cut it's tail off so it is straight down and just into the oil .
Should be 5 qts - not 4 .

Oil pump is newer .
How much oil pressure ?
Too much volume will cause a leak .

Block is no older than 35 .
What is the spacing on the main cap studs ?
It is vented [ the hole you mention ] .

Oil pan looks proper .

The oil pump drive gear cover can also cause your problem .

What are you using for intake-fuel pump stand and breather on to of oil tube ?
If you are using a 35-up intake and the tube under the fuel pump stand that is a bad idea with a 33-34 oil pan .