I have a '91 also and I just put in a radiator from the partsladi on ebay, $142 shipped. At the same time I put a chip from Marc Haibeck in. World of difference. The chip cools the engine down remarkably compared to stock. Both fans on at 205, both off at 200. Keys on all the time and no more CAGS either. I also put on Samco hoses from the Registry store and a 180 t-stat from NAPA.
thepartsladi on ebay, radiator auction
http://cgi.ebay.com/ebaymotors/90-91...3504QQtcZphoto
Haibeck's website with an explanation on the chip and what it does
http://www.zr1specialist.com/HAT%20W...on%20BFXBG.htm