I have a 1985 El Camino with no trip odometer. How hard is it to add a speedometer and odometer with a trip odometer?

Once you find a good working one and a new clear bezel with the hole for the reset knob, it's about an hour job to R&R your old one. You could find one in a Monte, Malibu, or El Camino up to 85 that'll match. The 86-88 Monte speedo will also work but the colors are different. Make sure you can attach your Vehicle Speed Sensor to it. They usually sell on ebay for $10-15.

Here's one on ebay now. (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4518319039)