As I understand DCJ parts numbering PN XXXXXAA is the first iteration of a part; next is PN XXXXXXAB; etc. Any part with the same numeric designation is interchangeable with any other part with the same numerals regardless of the alphabetic suffix; sometimes the differences between those parts is a minor as a different supplier but sometimes the difference is that AC is an improvement over AB (ex. gen 1 fuel filter head vs. gen 2 fuel filter head - latter has a better fuel heater element). An RL prefix is a remanufactured/rebuilt part. I would have EXTREME reservations about a dealer attempting to sell you an RL142797AC rebuilt turbo; as far as I know there is no such thing. That's not to say that some independent vendors do not rebuild our turbos but those vendors are not Garrett and I doubt they are Mopar suppliers.
Thoughts:
1. why do you think your turbo "went"? I ask as there are several things that mimic turbo failure but are not; usually much cheaper to fix.
2. yes 5142797AC is an exact fit replacement.
3. of course you don't need an exhaust manifold. They don't fail unless they rust through.
4. best bet for parts is idparts (
http://www.idparts.com/) - new Garrett turbo, oil supply line crush washers, turbo to manifold gasket, oil return line gasket and push gasket should be under $1,200 delivered (a bit more if your airbox to turbo hose has rotted just in front of the turbo). I wouldn't mess with the OEM style pinch nuts - 4 good grade 5 nuts and 4 lock washers are fine and available at any parts store.
5. it's an easy "weekend" job for anyone with basic tools (screwdrivers, pliers, decent metric socket set with extensions is about all you need). I say a weekend job simply because you need about 1 day to SOAK the turbo to manifold nuts in like PBblaster so they come off without breaking the studs - trust me on this I know. Actual job time after soak maybe 5 hrs or less if you know what you are doing.
If you want a how to drop me an email - not a PM.
PS - like Mountainman hints. Add your location to your signature. Lots of us are around with tools and at least some experience.