Unfortunately, no one make a lift kit bigger than 6" so you'll have to add a body lift if you want that lift height. The center driveshaft support is deigned opposite of newer trucks in that the bearing sits on top of the cross member instead of below. You can't put a spacer on to decrease the angle. A 6" already puts the driveshaft at a tight angle. I have a 6" lift kit, I understand.
I have a Rough Country 6" Lift Kit on my K3500 SRW and it's great in terms of overall installation and quality. It holds up well in the rocky and steep Colorado mountain 4x4 trails, but there's a few places it could have been designed better. I've heard great things about RCD, and I almost went with a Tuff Country lift kit, but it was harder to get in the time crunch I was in.