Hi lynnandtina, I happen to be building my 56 panel on a 72 chevy c10 frame and the cross member that you are talking about can be purchased as well as the trailing arms. The hoop in the cross member has been altered for a lowered truck. You can check them out at www.classicperformance.com and also at www.earlyclassic.com , If you still require measurements I will gladly go and crawl under and do so. I watched the show Trucks tv when Stacy David built Copperhead, a 68 chev c10 short wheel base, it was said that the hanger bearing could be elimenated if you shortening a long bed to a short bed, and early classic sells a c channel that fits perfectly inside the frame. I hope that htis helps.
John

 

Modifying the crossmember like the extreme drop one at early classic is exactly what I was talking about.

 

I up loaded a picture in my gallery. The clearance issues will be side to side, not up and down. There is 8" between the mounts, not alot of room to cut any material away to make wider. It was nice how the crossmember just slid into place though.
Lynn

 

would it be easier to get another 9" rear?

 

I have 2 housings, one is the correct width, another that would need to be shortened. I'm still debating which one to use. Shortening the one would align the pinion up, but then the engine is still needing to be offset for clearing of that big steering box. Right now I'm thinking using the 2 piece driveshaft just might be the easiest way.