These motors will run until you break the carbide face on a valve lifter and wipe that lobe off the camshaft. Then you're borrowing the cam and a lifter from a spare engine. Could happen tomorrow, could happen in 20 years.
You have to stick to an E7, you cannot use an ETech "E7". However if you had all the right components plus the know how, there's no reason you couldn't transplant a running ETech engine into the truck... But I wouldn't.
What failed, the head gasket? If that's all, then I'd just be pulling that head and replacing gasket. Better to stick with an engine you know is good (albeit with a lot of use) than trade for one you don't know...
