Sounds like a solid plan. Shoot me a PM if you do a build thread so I'm aware of it in case I don't see it. Definitely interested in how the 4.0/turbo setup goes. We are at the dunes quite a bit, you'll definitely have fun with some good HP in the sand!
I run a 30 with Yukon shafts in it and some good HP. Never had any issues, but the real hard abuse is always done in the sand.
434 pump gas SBC with an NX/HVH plate system
th350/Coan 5,000 converter/Dana 300 tcase
Dana 30 front with 4.56's/Dana 44 rear with 4.88's