I think if one is looking for an easy going, very sound, uncomplicated giant breed, Shilohs probably aren't it. They're mostly very big GSDs with some Malamute and maybe some livestock guardian mixed in. And possibly, maybe some wolf. None of which would make me think one shouid expect a people/dog friendly dog who isn't prone to being guardy or SSA.
I just didn't understand the possibly maybe some wolf comment in reference to two dogs that had bite histories. Because agreed, the oversized BYB GSD and BYB akita in there probably contribute a lot more to unstable temperaments than anything. Especially a wolf that may or may not have been used who knows how many generations ago.
That said, I have met some really sweet shilohs that were more stable than a lot of dogs. Have no idea on the general health and activity level though. If someone really really wanted one, there are a handful of dedicated breeders out there that are doing the right thing for health testing and being picky about temperament if you take the time to look.
To the OP, greyhounds and borzois are probably your best bet for healthy long lived giant breeds dog. NGA greys have a wide range of heights from 23" to 35". Both breeds generally make it past 10 years, have healthy joints and things. You'd want to research the lines because osteosarcoma can happen, along with a few other catastrophic health failures.
I'd avoid the other giant hounds like irish wolfhounds and scottish deerhounds. It would be an unusual blessing if your dog lived to be 10 years old, much less without any health catastrophes along the way.
What about malamutes? There are certainly unhealthy lines out there with orthopedic problems and stuff, but I've known several dogs that lived into their late teens (15-17 years). It seems like as a breed they're generally healthy and longer lived. And while they present their own challenges as a breed, they're nowhere as sharp and guardy as the LGD breeds.
ETA: I'm a derp and shouldn't comment at 1am.
Just re-read the comment about your dad getting a rad shelter dog. Good luck! I bet he'll find someone awesome when the time is right.