Mikael,

I would also check the harmonic balancer very carefully. I don't think the cams can be off by that much and not bend valves.
The balancer is mounted to its hub with rubber and after 18 years it could have slipped thus giving you a false reading. That in itself is not bad, but now if you set everything up with it off, then you will bend valves the first time you turn the engine. You can look down into the spark plug hole of #1 cylender (or have someone else look for you) as you turn the engine and see if the timing marks are a TDC when the piston is as high as it will go. You can rock the engine back a forth to get as close to TDC as posible. If this is off by more then a few degrees, the harmonic balancer has slipped and will need to be replaced before anything else is done. good luck.
I also have a 84 500 SEL with 250,000 miles and it still runs great.

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84 500 SEL (307,xxx miles)