Starter mount could be broken - take a look at the starter mount... Engine mounts could be broken clean out from wreck. What's behind the water pump - you know this from the teardown you did. Last couple of Elk Ole Patch slaughtered pounded the water pump shaft into the timing case cover. Behind that is the cam gear, possible bent cam snout, shattered castings on the block...
You can't see the wreck and the fact it did or did not hit a brick wall.
Cast iron like the block doesn't bend: it cracks, breaks, or shatters like the water pump did. My project truck I bought a $200 6.2 local and the heads were the only good part on it as the starter busted the block. The rest of the stuff is a PIA to resell on CL or fleabay, but, I have my $200 back from it and "free" heads.
The least "pain" to get up and running is getting a military surplus 6.2 from Ted's because a 6.5 is just a punched out 6.2, ask them to put 6.5 heads on it or if your heads are good use them... Again 6.2's are the unloved cheaper engines because everyone wants a 6.5 and overlook the cheaper 6.2 stuff. With a stock turbo you don't even need more than NA precups. (Salt in wounds will your son tear it up before it's time again as he learns the hard lessons of life? My age and I still tear engines up...)
Or get a 6.5 from Teds for the ~$1500 more. These surplus engine have half the miles (~30K), are tested and warrantied, and military maintained. Rings due to use may be toast from heat - running hot in a Hummer.
~$500 6.2 Shipping was "free" due to Black Friday sale...
$2000 for 6.2. Teds
~$100 diamand precups and 6.5 heads were just luck
$600 head work that wasn't really needed, but, as I run high RPM due to a Yank stall new springs were a must this time.
$200 gasket kit from parts store
$6.2 ring set are cheap NOS on ebay
~$500 TotalSeal Gapless rings
$100 for 8 NOS 6.2 pistons - maybe less I mentioned 6.2 NOS eBay was cheap, right?
$160 to coat the piston tops
$ARP head studs or new TTY head bolts.