You're lucky lol I'm having to do external oiling to make some Edelbrock LA heads work on a late 5.9L Magnum block. Pretty straightforward other than that, might have to mill the intake faces to make the holes line up. I'd recommend taller pistons to go with those J heads as well, what is the chamber volume on those?
@RogerRamRod Usually if you can get a Magnum short block in good shape (I pulled one out of a 2001 Ram 1500 at the junkyard) the roller lifters can be reused and the stock cams in both the 5.2 and 5.9 are much better than the stock LA truck cams. I got a custom roller Racer Brown grind for mine since the stock lifters are in great shape but replacements are expensive. Also factory machining tolerances were a lot better on the Magnums and they had much lighter pistons, most of all the multi-port EFI keeps the cylinders fresh even after 150k+ miles unlike carb'd engines getting raw gas poured down the intake on cold starts from acc. pump, choke running too long, messed up carbs leaking fuel etc.