If narrow band will do, that is a good suggestion. Pull any 4 wire sensor (or better yet get a couple) from a late model wreck for $10 or so, and get a guage for $30 or $40. You will only need 2 wires from the guage to the sensor so you'll have to wait for the sensor to warm up since it won't have heater voltage, but that's no big deal.

In the right hands, the cruise can be tuned as well with the narrow band as with the wide bands.