I don't have perfect pass/GPS/etc., so hopefully some of the others will chime in on this. However, replacing the gauges takes someone with time, patience and no sense of claustrophobia!
Your '99 21 might be easier to access with the observers seat up and out of the way. Move the drivers seat all the way back, use a flashlight to find a hand-hole under the dash to access the back of the gauges. Most everything under my dash was black, so it's hard to have too much light. Carefully remove the electrical connectors by lifting the lock tab and gently working the connector back and forth until it pulls off. It's been a few years since I did this, but I think you'll need a small wrench to loosen the nuts to pull off the rear retainer. I think the gauges slide easily out the front from here.
Consider taking a picture of the dash and/or drawing a diagram to help you remember what came from where. Also consider a fan - it makes the heat a little more bearable (in the south), and mosquitoes catch hell in a gale!
