I'm finally back into my car after a long break. Engine guys, please HELP ME SOLVE THIS ISSUE!

440, 727 TF, TTi headers, Eddy RPM intake, cast iron heads. New rebuild that sat three years, installed and run in, rings seated. No leaks. Readjusted the rockers and put valve covers back on with new cork seals. It started leaking and got progressively worse. Oil has been gushing out the drain vent at the bottom of the trans (727TF) inspection cover. I checked around the oil pressure sender. Dry. Checked the back of the heads. Didn't notice any oil at the time. Because the motor had sat rebuilt 3 years before I fired it, some suspected the rear main seal. I replaced the cap and seal with a Mancini billet unit with Viton seal, added a hemi pan and pick up with a windage tray/seal and filled her up. Leaks just as bad. The last time I started it, the headers smoked and I found that the valve cover bolts were a little loose. Noticed a drip on the driver's side headers. Tightened them and not thinking they could be the cause, I pull the transmission to check the cam plug. The plug is dry as a bone. DAMMIT. The upper part of the bell housing is dry. The TQ converter doesn't look like it's slinging oil. It's not dripping at all the crank flange is dry as well. Zero drips. Looking at the bell housing-to-engine mating surfaces, both are absolutely oily from the starter height down and the starter too is very oily. SO. I get the light waaaaay back there and yep. There's oil dripping off the back of the heads. It was indeed leaking at the valve cover gaskets and onto the headers. This and the oil on the starter is becoming my red flag.

For those experienced in chasing this issue, tell me. Under engine pressure, can oil leak out the back of the valve covers and sneak down the back of the block and enter the bell housing via the starter hole? It seems far fetched, but I am out of guesses. I just never suspected that all that oil could drip down the block and get past the mating surface of the trans. It's a lot of oil. I mean, 5 minutes and there's a half quart and it's leaking like a sieve out the inspection cover. And it's on both sides. My big mistake was not running the engine after I tightened the valve covers. The engine runs like stink. No bog at all. Roasts the tires in a blink, so I eliminated a head gasket leak, but who knows? Please entertain me with your thoughts. I want to nail this BEFORE the trans goes back in. Valve cover leak, or???