If you did not feel an out of balance driveshaft then you were completely oblivious to what the vibration is. ... I would not believe that a bad driveline would crack a block.
There are vibrations that can be felt, as well as unusual people like yourself perhaps that have driven a zillion miles and can feel everything. I'm not as experienced as you, but no newbie to mechanics and vibrations either, and I COULD NOT TELL even when paying attention for it. Whether you believe it or not there is no other plausible explanation as to why the block cracked, and the military engineering reports came to the same finding. What I said in my previous post is that it is foolish to hope you'll feel it, because the results can be very expensive.
Your previous posts say you used neapco joints and not spicer and bragged about those locking tabs. Like apparently you had never seen them before. The locking tabs come in the cheap spicer SVLs that are mad in china. But not a genuine 1610, 1710 or 1810 joint assembly. They do not come with them. Period. I can take you to the spicer warehouse and you can look thru every box till your tired and you wont find one in a heavy joint produced by them. Along with the trucks that run them everyday without a tab. I am dragging 78,000lbs down the highway and there isnt a one on this truck. . So the question is. Did you replace your neapco joints with spicer then?
Correct, I had to replace two of them because I had some friends helping me when we were doing the axle gear change, and they dropped some of the roller bearings in the dirt. I don't care how many warehouses you're going to take me to, I'm telling you the two Spicer joints came with them in the box. You were insinuating that because none come with them in the box, they must not be good/important/something, so I'm rebutting that by saying many of them do come with them in the box and that's poor logic.
I really like tab washers (as well as lock wire, castle nuts with cotter pins, etc.) because they never fail, except when corrosion or physical damage have occurred. I use them in a lot of my designs. I had never had tab washers on u-joints before, and I was definitely excited to get them! Locking adhesive (e.g. Loctite) works nearly as well, with the exceptions of oily/poorly-cleaned fasteners and hot environments, and the annoyance/labor of using fasteners that have it applied (once it has dried). Locking adhesives aren't bad, and I specify their use quite often too, but the mechanical locking methods are just better.
You may be some type of engineer or just try to expand your knowledge by reading alot but that is alot different than real world useage and knowing what you are dealing with in a hands on basis. Alot of the threads you have started are just information gatherings cause you are or were timid about hands on. Similar to the op here. He has posted threads about common failures, rebuilding the 3116 due to excess blowboy when he doesn't even know the proper of allowable blowby. Not to mention not driving it till then "weak links are fixed" no wonder its got blowby if it hasnt been driven and just idled around.
Enjoy your trucks. Dont worry about the what ifs and what coulds that other people have had happen. Its paranoia really. If stuff breaks during operation. Fix it. Simple as that. Wear and tear maintenance is far less than lack of useage maintenance.
Not sure where you're going with this, but I think you're hearing what you want to hear. While this is the first and only military truck I've owned, I've never been timid about hands-on. Yes I am an engineer (for air, land, and sea vehicle mounted equipment), so we do a lot of work and testing to understand what is actually going to happen with things like vibration, locking adhesives (and other types of locking fasteners), pressure hoses, mechanisms, etc. Shade-tree mechanics and field-fixes are dangerous things, because they don't really "know" (e.g. don't know that Green and Blue Loctite are the same strength, is a great example). Sure, we engineers don't get everything right the first time, but we're at least trying to.