I think that your cooling system is okay from your telling of what you saw on the gauge. I would go to the NetReg site and look in the maintenance section for the write up on what Carter is talking about. Also in one of the back issues(?) of our newsletter there is an article about how hot these cars can get. Anyway, there are two write ups in the "How To" section, one is to do the cleaning and the other is the intake screen. There is also a write up from Gordon Killabrew on a reasonably reliable translation of needle position vs temperature on both temp gauges. I copied it out & keep it handy for quick reference.
When my 90 had about 14k on it I took out the shroud and radiator to do the clean up. I had done the air intake screen mod before I started using the car and you should have seen the debris the car collected in just 7400 miles! I should say that one of the many benefits of having a re-programed PROM is that people like Marc Haibeck make the fans come on sooner to keep the temps down even with the stock 180* stat. If you clean up the debris and do the screen and get a lower stat and do a PROM rewrite you will really see how cool the system will run. Our water pumps move a ton of water and the debris and the fans' programing keep the car running hot.
Here are some links:
http://www.zr1netregistry.com/ZR1_howto.htm
http://www.zr1netregistry.com/ZR1_faq.htm#30
Tom