Broken F350?

I guess I just acquired a '96 F350...

My father has owned a mildly lifted F350 for a few years. Last year he burned up the auto box and I helped him swap in a new "built" unit from some purportedly reputable builder. Holy hell was that a heavy MF'er. That lasted a few thousand miles up until early this spring when he calls me up and asks for help again. Evidently the adapter between the trans and the transfercase grenaded. He wasn't exactly sure why but we replaced it with an OE aluminum one. That one lasted a thousand miles or so? Enough for him to move to Portland from Seattleish area. Then it blew up again. It fractured completely around. He found an OE version that was iron and I helped him swap that one in. In the process, replacing all the ujoints with spicer versions. (front and rear drivelines + axle shafts) as well as new hubs/bearings and stub shafts in the front. Well it broke again. This time after only 30 miles or so. He said he had the truck on stands and nothing "seemed" to bind. But I don't know for sure.

Well, he got fed up and bought a newer 3500 dodge and now that his landlord is complaining he offered to give me the truck. Of course I said yes because who doesn't need a powerstroke f350? I just don't exactly know where to begin diagnosing the issue. He's said it sounds/feels like the truck is shifting into park and then bang and it breaks the adapter. I can't imagine a parking pawl would be strong enough to break an iron adapter but I could be wrong. He's thinking it's either the trans or a broken/malfunctioning TCM (which is built into the PCM on the diesels). I'm almost afraid I'm going to have to toss another adapter in, just to see how it actually fails to know for sure what it's doing. Now on these trucks the trans isn't supported, the transfercase has a crossmember/mount. Would misadjusted linkage cause something like this? 

Does the hive have any suggestions/experience with broken extension housings/transfer case adapters? I don't have the truck yet, he'll be towing it up to me this weekend so I can get my eyes on it.

Is the adapter where the trans mounts to the cross member?

I'd start by checking all the motor mounts,  trans mount, bell housing bolts and rear suspension axle mounts to see if anything can move around more that it's suppose to move. 
 

Once you have the adapter removed, check the tail shaft for axial or radial play. Measure the tail shaft, transfer case input, and space to see if you have sufficient engagement and also to see if any movement in the tailshaft is causing it to bottom out in the transfer case causing axial loads leading to the failure. 
 

The aluminum adapter is able to flex more than the cast iron before failing, so if there is movement in the driveline the aluminum may be absorbing some of the shock which would explain why it lasts longer. 
 

There are other people on here with more in-depth knowledge that should be able to provide more specific info beyond the things I suggested to check. 

Thanks. I know the transfer case mount is new but I have no idea the condition of the engine mounts. Hopefully it's something as simple as the engine torquing too much from broken mounts...

Is there alignment dowels in some of the mounting holes? should there be?