big oil leak

[low ufo]

I just put in my newly rebuild 428 FE bolted up to a new TKO. Lifting it into the car (at a @30/40 degree angel) I noticed it starting to drip oil on the front side of the fly wheel, thought it was just a loose oil pan gasket. Anyways, I only had help to put the motor and tranny in at the time so I continued with the installation. Before starting it up I noticed a good amount of oil on the floor and after getting it running and setting over night I had a large puddle on the floor!! It's not the oil pan gasket I checked this morning. The question is by tilting the engine during installation and it leaking like this would this be a common indication of a bad rear main seal or maybe a cam seal. This was a constant drip every 5 seconds or so during installation. If in fact it is the rear main seal all the posts that I've read indicate that I can leave the engine and transmission bolted up and just drop the pan to replace the rear main seal. Any suggestions or comments. LOW UFO