I would like to install a ARB locker rd74 10 bolt rear locker in my sidekick,problem is i removed the third only to find that im using a 12 bolt pattern.

Where could i purchase a 10 bolt ring and pinion 5,125 ratio from?

Can i not modify the rd74 to fit in the front diff?

I would like to install a ARB locker rd74 10 bolt rear locker in my sidekick,problem is i removed the third only to find that im using a 12 bolt pattern.

Can you return it and get the 12-bolt ARB?  That's what I hae in mine.  the 12-bolt ring gear is stronger than the 10.

Can i not modify the rd74 to fit in the front diff?

No.  The rear is a 7.5" ring and the front is 7'

Tell us what year, # of doors, and engine you have, as it's been tricky determining which have 10-bolt and which have 12's.

You can change out the diff case and flange cap to the 12 bolt style if you wanted.  You'd have to pull the whole locker apart, but it doesn't take long. 

You'd be better off buying a whole 10-bolt 3rd member with 5.12 gears already in it so you don't have to reset the pinion.  Grab it from a junkyard, since you'll be changing out the guts of the diff and the bearings anyway.  1992 and older should all be 10-bolt's.

Ya you could save your self a lot of time and money just by finding another 3rd with 5.12's already in it.

I cant swop the locker as its a second hand unit that a bought for a very good price.

I wouldn't want the locker to go to waste so thats why i wanted to purchase a 10 bolt ring and pinion, but if the 12 bolt pattern is stronger then i will have to retain my current 3rd with 5.125 12 bolt ring and pinion.

I already have a lockright installed in my current 3r'd i just wanted to install the arb its easier to drive on normal roads.

Like i said before, just buy a used complete third member with 5.12's and put the air locker in that.  The 12 bolt will be stronger, but not enough difference to worry about it.  How many people in sidekicks/trackers are breaking their rear ring and pinions?  The axles break first.

As i said before i currently have a 12 bolt rear with 5.125 ratio with a lockright in it.

I just wanted to utilize the arb 10 bolt third and purchase a 10 bolt ring and pinion so as to not waste the locker,i already have a spare 3rd that i can use i just need the ring and pinion.

So the trick question where could i find a 10 bolt ring and pinion 5.125 ratio?

AT THE JUNKYARD.

You will have to find a 3rd member in the junkyard with 5.12's in it.  It's a waste of time to pull the ring and pinion out of it just to install it into another 3rd member.  If you find a complete 10-bolt 3rd member with 5.12 gears, you'll just have to pull the diff out, remove the ring gear, put the ring gear on the ARB, then install it and set the backlash.  You won't have to mess with the pinion.  I was trying to save you a few steps and some money by suggesting this.

Thanks for the advise crikeymike , it's of to the junkward for me.Who knows maybe i can salvage some other spares.