Properly sealing timing cover to oil pan.

That's generally not a trouble area on a big block, because of the flat surfaces. I cannot imagine what it could be. I would say check the pan to assure it's not bent down, but the way the pan bolts to the timing cover......it would straighten itself out. Are you SURE it was coming from the timing cover at the pan? It appears your block is missing a locating dowel pin for the timing cover on the passenger's side. What I would do is get the timing cover back on with the bolts loose and install the balancer. This is the proper method for getting the timing cover in the right place without dowel pins. Once you have the balancer installed, tighten the cover and oil pan.