most Chevy cps's are located in the timing cover(behind the balancer). I'm not certain on the Celebrity, but it would be a good place to check. Answer On my 1986 Celebrity 2.5, it is beneath the intake manifold on the back of the engine.
Timing on a 1987 thru 1990 Chevy Celebrity 2.8/3.1 engine is controlled by the ignition control module along with the engine control module. There is no provision or specification for manually adjusting the timing on these distributor-less models.