Wagonboy,
I use a Thule crossbar and bike rack combo on my '85 wagon and can carry two road bikes and a small mountain bike no problem. Sorry, I don't have the part numbers since I bought it years ago and can't find the receipts. I got it at a speciality auto rack store. You'll not be able to use the MBZ crossbars as they are way too filmsy and not really meant to take much pressure. I clamp the Thule cross bars near the front and middle side rail supports (where they attach to the top of the car) for added rigidity. I can just squeeze three bikes on by facing the middle one backwards. The only negative is you'll probably want to remove the bike rack when you aren't using it because it makes a bit of noise at high speeds. By the way, I use the same Thule crossbars to clamp on a ski rack in the winter. I think they sell adapters for boards too. Good luck.

LRG

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold