Your Question isn't very clear. I don't see why you should have to have a new crossmember when you change mc/booster. But...

The main thing about changing the cross member is the alignment of the driveline. The output shaft of the tranny has to be parallel to the pinion shaft within a few degrees. There's a good article about it at http://www.classictruckshop.com/driveline.asp .


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