I think you'll need to loosen things up at the bellhousing to get the pan to drop. As Mel said - the front timing cover comes down across the front of the pan, but there are no bolts into the oil pan. Sorry I haven't been more help - my oil system is a hybrid of C parts and DC parts so I'm not sure which parts came from where anymore.
Below is the info I found in my service manual (I cut out the stuff for L series):
The adjustable ball type reilef valve is used on series C engines prior to 4209666 and is located in the pump body. Relief valve adjustment for a pressure of 30-35psi can be made by working through the oil pan inspection hand hole plates.
Series C engines after 4209665 and all other series have a non-adjustable plunger type relief valve that is located in the pump body. Normal oil pressure on C and D series is 30-35psi.
From the diagram in the service manual, it looks like a hex head threaded plug that screws into the pump body near the upper gear (if it's like mine I think this is brass?? - it's fairly large in the diagram so I'd think it would be obvious if you saw it - only other thing at that level on the pump is the outlet elbow) It has a picture of a relieve spring behind that cap with a piston like valve at the end of it. I'm guessing this is the fixed style. I would think if that relieve valve would be hung up in the hole or the spring is gunked up, it wouldn't allow for the pressure to release. I don't know from the picture which direction this would be heading - so I have no idea if it is something you can access from the hand holes or if you'd be better off dropping the pan. You'll need a helper (or a floor jack) to drop the pan.. or at least to put it back up!
Hopefully this helps. If needed, I can try to take a picture of the manual and e-mail you, or if you're not in a hurry I could photo copy what I have on the oil pump and send it in the mail. Let me know if you need anything else.