1996 Chevy 1500 Silverado 350 Vortec sbc. 120K miles stock. Ran perfect. Noticed a tapping sound coming from the left bank. Sounded like a lifter. Pulled the cover and all looked tight. Adjusted the valves on that bank and the tapping lessened but was still there. Later that day I noticed the oil pressure down around 40psi (normally runs 60psi). I changed the oil and filter with 20w50 (from 10w30). The tapping noise was a little less and pressure was up to about 48psi. Two days later, steam blows from under the hood and the crank is filled milky white. I assume it blew a head gasket. Pulled the engine out and decided to get a long block from Autozone. When I pulled the distributor cap I noticed the rotor only had one screw holding it and was spinning off center wearing on the dist. housing.
Could the timing cause a head gasket problem?
How about the valve adjustment? I went a 1/2 turn tighter on all the valves.

-Kevin