The cam in my 68 C20 with a 327 was bad when I bought the truck. After getting the carb to run right, it had been sitting for 5 years. I went to adjust the valves and it was obivious the cam was flat, as little as a 1/4 inch of movement on some of the valves. I had done a compression check on it and it wasn't great 110-130 about what I would expect for 116k on the motor. After changing the cam the compression even outand improved a bit 120-135. The truck ran like a top till about 2 months ago and a head cracked Ouch! You might just pull the valve covers, put a straight edge acros the valve springs (valve seat wear, start it up, set the idle down or turn it over by hand and check the minimum spring height.
Larry

I don't own a vehicle that isn't old enough to drink.