Rear main replacement without removing oil pan?

My neigbor is restoring a M151, and I am his mechanical advisor. (He doesnt have much mechanical experience, so he bribed me to help with a 12-pack of Mountain Dew. Dont tell him that I would have done it for free!)
We have the engine and gearbox removed and separated. He has a new rear main seal, but no oil pan gasket. I was wondering if anyone has replaced their rear main without removing the pan? Do you have to loosen the main bearing caps to change the rear main seal?

No you do not have to remove the oil pan nor the bearing caps to remove the rear manin seal. A few years ago I use to have a neighbor who worked on the same motor in towmotors (fork lifts) and when I had a leak in mine he replaced it for me this way. He took a small punch and centered it on one side of the seal on the metal part. He then gave it a good solid wack with a hammer. This cocked the seal where he could take a screwdriver and pop it right out. Then he tapped the new seal gently back into place. I think he coated it with oil first before sealing it, but its been 11 years so I don't remember the deatails. Just about the same proceedure as replacing a wheel bearing seal.
Joe

That is what I was thinking I was going to do, but it's better to ask those with more experience than I before starting. Thanks for the help!