ok, here is the deal, I built a 431(440 source kit and stealth heads) for a guy and I used the flat top pistons and stealth heads with minimal decking(only to clean and make flat), and a lunati cam .226/.234@.050 dur. by .494/.513 lift, RPM intake/thunder series AVS 800 carb, HV oil pump, deep oil pan, windage tray with felpro gaskets.
when I first fired it up, lots of oil leaks, pulled the engine and replace the cam plug, 2/3 of oil leak gone. Next, I pulled the oil pump and cut 1 coil out of the pressure relief spring, and replaced the gasket...still has 80psi, no change. And replaced both valve cover gaskets from rubber to cork, even better, now only leaking from the rear of the engine. Pulled the engine again, replaced rear main seal, and both pan gaskets using Mopar black ATV, new oil 10-30w (broke it in on 20-50w VR1)also redid the oil galley plugs with new teflon tape. Ran it for 15 minutes in the driveway car facing up towards the garage, and after about 10 minute it started leaking from rear of the engine, but very little (like the size of a silver dollar after 15 minutes).

80 psi oil pressure at what RPM? I would expect that at 8,000 rpm! 25 or 30 psi at a fast idle is more than enough, IMHO

cold start up and warm about 70psi, a buddy of mine who races bb mopars says 80 is fine, 120 isn't. I had 80 in my 600hp 446 with eddys with no problems.

I'd pull the eng & do the rear seal again & get that taken care of. I know it's a pain but it unfortunately has to be done again because you will never be happy with the drip & it likely will get worse. 80 is slightly too high & unnecessarily wears the intergear etc tho it ain't a dealbreaker being a bit too high but with the easy access of the BB spring I'd shorten it some more. 8-10 psi per 1000 rpm is plenty. I'd be wondering more about the rest of the oiling mods

may be that your pan is not fitting good . could be bent or warped . check the fit all the way around . check the rear seal flange areas and the seal areas on the block/cap . without knowing what windage tray is in use , can't rule out it causing a pan/ fittment issue . my opinion on oil pressure is that 65-70 psi cold is the most you need unless you are seriously racing the car and, that's if you have really tight clearances . using 20-50wt, 35lbs @ 1200rpm hot and 55-65 @5,000 rpm is ideal. more pressure will only over stress the oil pump drive, add extra heat to the oil and can keep the system on bypass ,which will not filter the oil. also, most higher output oiling systems have restrictions to keep some oil in the pan at higher rpms. if the engine is new and really tight on bearing clearances , you may need to use a thinner synthetic race oil with an additive as it will flow better when cold ,and, better deal with heat as well. cutting the spring is the opposite to matching the oil viscosity.

Do you have main studs or bolts? Sometimes the seal retainer rests against the rear main nuts and doesn't allow it to seat fully. If so, then clearance w/grinder.
Chased that one for a while

bolts on the rear mains and its a 440 source deep pan, but used stock windage tray. I spoke with 440 source today and they recommend taking the aluminum saddle and milling .010 from the bottom where it mates to the block, and backing the pressure down.

Good stuff what eK3 said, get the viscosity right first then mod the spring as needed

Valve cover gaskets.....Moroso (rubber over steel) I will not waste any more time with cork or rubber.

Rear main seal. Source crank has no knurling on the seal area.Cut the retainer.Use the double lip Viton seal or a rope seal.Black seals are not as pliable as they used to be (Mopar and Fel-pro). Don't forget to seal them on the back side.Offsetting them will also help but I have sealed them either way. Use the side sticks from Hemi-Haynes or stock ones if you can find them.Seal the back of the retainer where the sticks are after everything is set. Do not use the silicone to replace the sticks.

I did go from 20-50 to 10-30 and now oil pressure is 80 cold and 60 warm at an idle.

There is some addit'l info regarding straight weight vs multi viscosity oils to be perused (I ain't up on it but someone will chime in & help you) but you're headed in a good direction

I am going to try a different seal retainer and have it milled 0.010 at the base, better gaskets, maybe the felpro race rear main seal, a new windage tray and a stock oil pump. I will clean everything with brake cleaner, lift the rear of the crankshaft up a little to make sure its very clean, dry and oil free. And I will use mopar ATV silicone.

How about Mancini's rear main seal retainer??

http://chucker54.stores.yahoo.net/bilrearmains.html

Do not use synthetic oil on a fresh build, if the motor was not specifically built to run on synthetic you are going to have ring seal issues.

If you have oil leak issue with regular oil it's going to be worse with synthetic.