Oil Leaks

I have a 69 Chevelle convertible SS 396 Clone. It's got a 72 454, headers, competition cam high rise manifold with a holly 750 carb. TH350 transmission. I have had a few oil leaks, but the one most concerning is a slight oil leak along the side of the block coming from the spark plugs. Can anyone tell me if this is a serious issue, what caused it and how to fix it.