[Randy Mosier]

Turn the crank back and forth by hand while watching the rotor. You shouldn't be able to turn the crankshaft any appreciable amount before without seeing any rotor movement. 150K, it's probably time for a chain. I just happen to have a brand new McQuay Norris timing chain set that I bought at a swap meet two years ago, still in the box. It's for a small block engine, but I think the 4.3 uses the same parts.
If you plan on going to the car show in Haltom City this evening or tomorrow, email me, I'll bring it there, and it's yours. The car show is at a city park and little league field near the intersection of 820 and Denton highway. I'll drop you an email also.