The upper seal was rope on my '73. I replaced it with the rubber one. I can almost guarantee that yours is rope, too. They are no more difficult to replace than rubber, but having a rope upper and rubber lower might be tricky to seal. You could try RTV at that junction, but I don't know that the rope being saturated in oil will ever take the RTV completely. It might slow the leak down significantly, though.
Either way, just taking the rear main cap off won't do anything to get to the upper, because it's above the crank, in the block, itself, along with the rubber blocks that seal the main cap to the block and the lower, within the main cap.
The issue with the pan isn't what is under the pan, it's what is inside the pan, down below the bolt/ gasket line that will make your life hell, with the engine in place. You have to get the pan down far enough to clear the crank at the very front, but even if you rotate the crank so that the counterweight for the 1/2 piston journal is up and out of the way, you still have to move it around the pickup in the sump.
You shouldn't have to take the engine out, or the water pump/ timing cover if the rear main lower seal is what is leaking.
Do you know what your timing chain looks like, or how long ago it was changed?
The reason I ask is that if you've got the car apart down there and the car is out of commission, it would probably be a good idea to change the chain. A rear main seal leak is usually not the only part of the bottom end that needs maintenance, when it goes, unless it's a fluke.
I think it would be wise to do upper and lower seals, or just wait on it, save some cash and pull the engine to clean up and put new gaskets on everything, with a new chain, all at once.
