Effect of oversized tyres on gearbox

I like the idea of swapping crown wheel and pinion but have been put off by what I imagine it is going to cost given I don't know how to do it myself. Can you give me a rough idea of the cost involved?
Cheers.

damn puter logged me on as go_oofroad again, oh well,
you would be looking around $150-$200 a diff for set up, + remove and replace, if you cant do the easy bit.

But if the price puts you off, you should probably stick to the tyres you have, because 315's will add cost in wear and tear, fuel consumption etc.

Thanks, was thinking 4.3 or 4.6 and 285's. I've already spent a bit on it and the wife is getting harder to convince.

what what what?? $150-200 for a new gear set??
The cheapest price I found was $530 an end, and that was after scouring the country from west to east.
The alternative is to put in some new ratios in the gearbox, but that involves dropping the box, which I swear I will never do again on a cruiser. The added cost of the bigger rubber ($100 more per tyre for an extra 2" diameter seemed common) and the cost of mechanical parts needed kept me at 33"s.
A local 4by shop here runs a diesel 80 on 35"s with stock running gear- They have reported no dramas on the drive train. Just get a caster correction to fix the front diff angle or you'll bust uni joints I am told.

the gear set is extra......