I'm still hunting down parts and wanted to track some of my findings here. 
I'm looking to upgrade to a steel housing. 
I have a 1997 Geo Tracker (4 door) 1.6L MPFI 16V SOHC  5 speed man. with 5.125 gears. 
From reading Eric Bewley's posts I found that I can get a steel differential from a Grand Vitara or XL7, but I'm having a hard time finding one with the same gear ratio. 
I did find that these years have the correct gear ratio; 
99-03   Tracker   1.6L MPFI 16V SOHC   Auto or manual   5.125
99-03   Vitara   1.6L MPFI 16V SOHC   Auto or manual   5.125 
Should I draw the conclusion that ANY "Manual" Grand Vitara or Tracker 99-03 will be a direct bolt-in with the same gearing?  Crossing my fingers 
