I drive the 420 SEL and ran into the exact same problem last week. You are correct, the bottom bolt will not come out by any means without removing the balancer or pulley.

The 27MM bolt on the crank is right hand threaded like normal. I first attempted to remove the pulley and balancer by themselves when I did the work, but the balancer would not come off and of course it doesn't have any way of pulling or prying loose without damaging the oil pan.

When I went to remove the entire hub assembly I removed the radiator and put an impact gun on the 27MM bolt. I didn't manage to remove the bolt as my gun is rather weak but instead managed to vibrate the balancer loose with it. You might try this if you have access to air tools.

If you don't have any other way to work around this and really want to remove that 27MM bolt I suggest putting a socket on one end of a breaker bar and the other end on the ground and bumping the starter. There isn't any way I'm aware of that will get you more torque than that. I'm assuming you've already removed the distributor so no need to worry about the engine starting. When you go to replace the hub assembly put the whole thing in the oven and heat it to around 200 degrees F and then quickly take it from the oven and slip it onto the crankshaft. This should make life a little easier.