I would recommend going with the heavier bundts used on the 123 cars. There was a reason the factory put the 5.5" wheels only on the 240. The event of a failure of the rim is unlikely but consider when it might occur.....it will not occur when you are driving along on a straightaway it will occur if you run over something on the highway or are cornering hard to avoid an emergency and hit a chuckhole. In other words failure will occur at your moment of maximum need.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.