Electrical problem

I have a 1969 Pontiac Le mans, 350 2bbl, it has about 169,000 miles. The car will crank but wont start.I just changed the coil because I figured that was reason. Because I removed the plug from the center of the coil and sometimes it would spark other times it didnt. From what I uderstand it should always spark. So I replaced it with a MSD blaster II. But I have the same problem. But instead now when I start the car it doesnt even spark once in awhile. My dad removed one of the spark plugs to find that not even the plugs were getting sparks. What could it be? It will crank forever but just will not get on and turn completely over.