I'd think it'd be fine. The ck has quite a bit more lift capacity, as you point out. Even if you go to r4s, the 4wd should compensate and I bet you'd end up with about the same amount of pull. If you go with r1s, you'll have more pull than the 8n, I'd think.
I am going with R4's. Now if I can find the 8N a new home,its off to the dealer!