I haven’t found an LLY for more than 5g less than an LBZ with the same mileage so I’d be spending almost the same once I convert it.I'm saying money ahead on versus lbz. Head gaskets are and done on a lly... You can run into the occasional lly head crack.... No biggie replace with lbz/lmm heads. I don't know why you'd suggest you would do them every 100k. Buy the truck, drive it till you do the gaskets and stud the engine. Only tcm tuning needed to be done is shift points, and possibly lock up strategy which should easily be done. Plus do what they are told via efi live, and with head gaskets and 6 speed you'd be money ahead vs over paying on lbz.. which some models are still prone to gasket failures and then you have a higher probability of cracking a piston or snapping a crank. When you say lbz, I'm thinking you'll be spending 30k for what you want.
Buy a lly for 15-20 in mint condition, mod it to your likings
As I mentioned before I would have to rely on duramaxtuner to do the TCM tuning as I don’t believe normal folks can. Would need to research this some though. And ecm tuning an lly is not my forte.
You have a point with lbz pistons but lots of lly’s broke cranks too. And I’d say it’s 4:1 for lly head gaskets over lbz. Everyone I know that’s kept an lly for any length of time has had to do them about every 100-150000 miles. I don’t know why. A few warped and cracked heads too but probably related to driving with bad gaskets imo.