You might want to consider leaving the front drive axle just for the ride and stability features. I am currently in the process of building a triple slide 30' box on a freightliner columbia. We wanted the sleeper for two reasons #1 We can accomidate 2 more beds in this area if we need them and #2 it is laid out for 2 lay-z-boy style chairs because it always seems like everyone is crowded around the driver when you go down the road. I added 10.5' of frame in the middle and 8' behind the axles. I tried 6' but it just didn't look right. Also I matched he contour and angles of the sleeper all the way to the back instead of squaring everything off. Hope this helps.
