Excel,
Judging by your questions, you need to have a pro do it...the tools are expensive and you need to be accurate. The guys who do 4-wheel off-road diff's are good, figure @ $1000. including the locker. I went Tru-Trac, which uses "throw-out" helix gears to lock, vs. clutches. I assume you have a 9 inch?
scratch
