Update: I cut a piece of 2 x 3 and pounded downwards from above with a heavy log splitting hammer. Then I crawled underneath and pounded forward while again using a piece of wood. The support moved pretty easily; it only took about a half dozen blows and all was well. The belly pan is all ligned up again and screwed in, though the left portion of it has been torn off. I'll add that to my list of things to get...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280