This is my take. First, on each side of the block deck, there is a passage from the cam to pass oil to the head rocker oiling passage. On either side of these oil holes, are coolant holes. My choice is oil going into one or both water holes, thus your transition point, but why? You already identified why, the head (or heads) are not being tightened properly, thus creating a leak path. So, look at your iron chunks, and look INTO the head bolt holes for a path to water. Mopar head bolt holes are blind and should not get to water. Not a deal breaker as the bolt seals the hole for the most part. The cause of the failure is likely the wrong bolt set from ARP for the aftermarket heads and they bottomed out, punching the holes into the water jacket. Or, the head hole boss is not the correct height (low), also punching the hole bottoms out. At this point, the block could be compromised, or maybe not. Studs might be a way out as you can ensure that the heads will compress the gasket properly. Use a tap to chase the bolt holes to the very bottom and blow them out well. Install the studs while paying attention to the stud shank (unthreaded portion) and it should be below the head hole boss. Install the washer dry as DVW said and apply ARP lube to the top of washer and stud threads. On a side note, put a SMALL amount of oil on the block threads so it will not hydraulic. I also scuff the bottom of the washers to roughen the surface to prevent spinning. A tip I picked up from ARP LS head stud kits. Once properly tightened, your gaskets should crush properly and seal the leaks.
