Re: single spinner to LSD conversion
You could just swap the centre and keep ur old ratio. I got mine for $550 + $200 fitting. I think it might have been a rebuilt one. You might be able to swap the whole axle for less though, but the centre would probably have had more wear.
One thing you might want to ask about if ur getting a new centre is a "Lock Right"? It's a locker and I've been told they cost $650, but are a lot stronger than the standard one. The standard ones can crap themselves if u hurt them on a regular basis.