Where should I buy a spare cm870 ?

[tree98]

I think i want to buy an 870 to have rebuilt by one of the guys on here (mr. Hag or gearhead) so that I have an engine ready to put right into the truck when mine shits the bed. It's an 06 with 400k mi. And 22,000 hrs. It's a log truck with a log loader mounted to it so it has hours on it from loading and unloading. As far as I know it's never been apart and I just have a feeling it's gonna blow a head gasket or who knows what and then I'll be down for weeks or longer. So should I buy a running engine from a place like Adelman's and have it redone or should I buy a long block from cummins and have it taken apart and liner height, piston rings checked etc. Opinions anyone?