If you look at my post immediately above yours, you'll see the track widths for 1999 models:

Drive, track width (front/rear)
2wd 55.0"/54.6"
4wd 57.2"/55.1"
ZR2 61.1"/59.0"

With this in mind, if your goal is to get the track widths to be the same then the least aggressive way to accomplish that is to install on the rear only, 1" or 1.25" spacers. By only installing them on the rear, you are not changing any of the front end geometry which I, with nothing else than my gut to go by, felt likely a good thing to avoid doing. And ditto on using only high quality metal, studs and to the spacers being hub-centric in design.

I installed 1.25" spacers that I purchased off of eBay. One reason I chose the 1.25" ones is that I would know that the spacer would be thick enough so that the lug bolts would not stick out from the spacer.

Here are pics of the ones I installed:


The box



The spacer before install



Spacer installed