Hi, I just purchased a GTS 6.7" rear axle and need to have the housing shortened and the axles re-splined. I noticed that the housing gets narrower from 3" to 9" (when measuring from the back of the caliper bracket). Can anyone tell me if this narrow section cause any problems with shortening the housing? Thanks.

It will be hard to find a quality axle shaft for that width axle. When you shorten the axle you take away the "twist" that helps the shaft absorb shock. You may want to look into a Toyota 7.5 housing as there are plenty of shops that sell custom parts for it.