Zeus has pretty much explained the solid spacer for me. Getting it shimmed accurately is also  important. I can put you onto someone in Melbourne who can supply the airlocker and fit it all up including spacer and ship it back to you for installation if you want. I personally don't have much faith in some of the fitters around and although the ARB locker is a great piece of equipment some of the employees level of skill can leave a bit to be desired at times.

The ratios available to you are 4.30, 4.625, 4.875 and 5.125 but the 4.875 is of no interest to you if you wish to fit an airlocker. I can't remember the number of teeth on each of them but I'll see if I can hunt it out as I have it somewhere.

More Problems.. any help any idea.  i ordered a arb rd 79 diff lock for this car. but the crown wont fit over the new arb centre, arb has had a look and agree..  i originally had a ratio of 4.3 in this diff. i then ordered a new crown and pinion of a 2ltl with a ratio of 4.875. both crown wheels are exactly the same and both dont fit the rd 79. the splines and 12 bolt patteren are ok. does any body know what the difference is with a rd88. HEEEEEEEEEEEEELP 7 wks of the road and still going backwards

C J YES PLEASE CAN I HAVE THE NAME AND PHONE NUMBER

I have sent you an email. As I mentioned in my previous post, the 4.875 ratio will not work with the air locker due to physical differences in the R&P.