Please help me diagnose this 273

Ever check the slack in the timing change? Something is making the timing vary. Has to be one of a few things. Bad distrib, doubt it I remember that one, loose worn chain, could remotely be slack in the oil pump drive gear, really not often do you see that. You do need to find out why two cylinders are low on compression. If any one you know has a scope see if you can put the car on it. Also a leak down test will let you know if the valves are bad in those cylinders.