This is an old unit isn't it? Have you got a link with the spec?
However, assuming it is a regular thyristor auto gun, it should work fine on a 40D. Obviously not TTL auto, but match the f/number on the lens with the correct setting on the flash, and away you go.
You'll need to use Av or Manual and the sensor/thyristor will sort the exposure. These things are not always dead accurate so you might need to compensate. Just change the f/number.