How to diagnose cam shaft?

[thelawdoc]

Gentlemen, I have a stock '66 C10 250 w/2 spd Powerglide & Rochester B. The odometer says 65k. Truck was starting and running nice until about a month ago when she began to start with great difficulty and suffered frequent stalling at red lights. I rebuilt the carb, changed plugs and wires, changed point & condenser, changed both fuel filters, verified good fuel pressure, new battery, fresh gas and good spark with wires correct for firing order of 1-5-3-6-2-4. The other day I finished up this tune-up by doing the timing and adjusting carb. I take her for a test drive, she starts up and runs great for about one mile. Then stalls. She restarts easily and runs nice back to my house with a couple stalls. I check the timing again. The rotor is off by 180 degrees! And I could not restart her. I check distributor gear -it is like new. No marks. I look down into the distributor hole and everything looks fine in there too. The belt is fine. I pull harmonic balancer and take off timing gear cover and the gears look pretty new, though my harmonic balancer does not look very good (the rubber is separating from it). Mechanic/buddy says my harmonic balancer is shot and cam shaft must be worn out. But I am not confident about the cam shaft being bad. The only other clue I have concerns the carb needle: when I close it all the way in during adjustment of carb, the engine does not shut down as I believe it ought to. Also, I did not do timing with vac adv plugged. Any ideas? Could it be the cam shaft (I hope not)?