1975 Chevy Blazer No. 2 exhaust valve

I just bought this vehicle and don't know the history. Engine is a re-man. The #2 exhaust valve is not opening all the way and is causing a backfire thru the carb. I have checked the adjustment and it is correct and the push rod is straight. Is there a way to check the lifter before tearing down the top half of the engine and pulling the cam to check the lobe? Thanks.