If I provide a remanufactured, OEM engine (v8, 5.7 liter), how many hours should it take for a shop to swap it out with my current (bad) one?

Every car is different. I'm glad you're deciding to go with a remanufactured, instead of rebuilding what you have or rebuilding a junkyard motor. The book calls for 22 hours to remove and replace. But, if they take the body off the frame, and then remove the engine, they'd actually cut the time in half (approx. 11 hours). But, they will either call you crazy, or just not do it. So, probably 22 hours.