Wow, didn't realize you had a unicorn MC 2500 with the 345. Although they've had quality issues with welds splitting, look into hooker blackheart log style steel headers for the 5.7. Swapping those would take an hour a side once you had the liners and tires off.
Do you really need a tune to run shortys? I'm not quite ready to go tuned yet but was thinking of getting BBKs with heat wrap and paint/sealed of course. Reason being my intake temp has been 95-125Â°F lately invthe Texas summer. I already have a magniflow y pipe and a flow FX muffler on my 2017 quad cab, 3.21 gears