If it is valve guides the smoke will be heavy after start up and then get light to none after running a while. Having good oil pressure on that engine only tells you that the oil pump is good. The bearings can be shot and knocking and have good oil pressure. Oil to the bearings comes from centrifugal force thru the spinning camshaft. It is sent thru the camshaft bearings to the main bearings. Little holes spray oil on the rods and the spinning of the rods catch the oil and forces it into the rod bearings. Compression is a good place to start.