I've heard of the "killer dowel pin" on the 5.9 and assumed the 4B suffers the same flaw on at least some models. There are quite a few different manufacturers of a kit to hold the dowel pin in there. You'd think that, assuming the KDP exists on all 3.9, that it would be more vulnerable to it with how much these things vibrate and jump around. Is there any information on which serial numbers of the 3.9 have the flaw?
Op, if you are going this far into the engine for replacing the mains, pistons/rings, and doing the timing cover to review the KDP, it might be easier to just pull the engine out and put it on a stand to work on it. Atleast on a 580, it doesn't look like it would take more than a few hours to pull it. It might save that much time being out in the open plus possibly being easier to do.