Mikes right, if your gonna paint it up, do it before the oil has a chance to soak into the pores of the block. Then you can clean up the overspray that the masking didn't protect from.
On the 383's, sometimes the rodbolts will snag the cam, depending on the rods, the bolts and the cam. I've seen some casting marks interfer inside the block....sometimes theres alot of shift here, there and yonder. Chances are things will clear, but I've seen things get crazy fast. But thats the reason for the small base circle cams, to get clearance. Anything closer that 1/4 can cause problems inside there. Believe it or not, that oil being flung around in there about 4000 rpm will foam the oil, which is not good. That puts bubbles into the oil, and will screw with the bearings....
With Alum. rods, gotta check everything everytime, with steel rods, its usually just the rod bolt area.