Well it was running but doesn't really sound right. Just sticking a screwdriver in the sparkplug hole isn't definitive. You could still be at the top but on the exhaust stroke. On the other hand, if you're not getting a strong push of compression against your thumb either time the piston is at the top, then maybe the cam isn't timed right. I agree with the suggestion to take off the valve cover and watch the valves work as you're turning the engine over. You should be able to see all four strokes and the intake and exhaust valves operating at the right time based on piston position. At that point, you probably want all eight sparkplugs out so you can turn it over by hand more easily with a socket on the harmonic balancer bolt.

So you installed the cam? How did you confirm it was timed properly? Did you use a degree wheel?