I need advice on changing differential gears in a 12 bolt 68 Chevelle. Should I attempt thiis myself or have a garge do it?
Lou

You need to know how to set the pinion depth to +/- .001 inch, set the bearing preload and set the backlash to +/- .001 inch of nominal. You also need to know how to read the contact pattern on the gears so that you will know what adjustments need to be made to the pinion depth. There are a few special tools that you will need for the job, like a dial indicator with a magnetic base, a press with a bearing seperator and a few others.

Pay a qualified person to do it!

Thanks for the advice. From the description of what is involved, I see this is not a job for the casual back yard mechanic like myself.