I'll try to answer all your questions briefly. To break the retainer loose on the top of the valve, tap the top of the valve stem a few times with a hammer. There are marks on the balancer to correspond with 2 cyls at a time to remove valve springs. I would just do the seals. I can't see a reason to do all the rest of what you plan. Keep the rockers in order and do only the seals or you need to acquire the special MB tool to set valve lash. Also renew the plastic parts that hold the oiler tube in place. If you don't, you run the risk of the oiler tube coming loose, the cam seizing up, and a valve getting bent. I recently picked up a beautiful 82 380SEL for $300 for that very reason.
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