How much horsepower are you shooting for with your 6.0? 400-450? What about headers?
I see 2 potential problems. 3" is fundamentally too large for the type of HP your mighty 4.3L was throwing down, depending on what you're shooting for with your LS swap, 3" into dual 2.5 out will probably be fine.
Resonators after the mufflers, I don't like. Get rid of the resonators all together and dial in your sound with mufflers. Resonators add a wild card to how the final exhaust tone will sound and I always recommend going without them unless drone is a huge concern (Could be one of the reasons why your 4.3L sounded like a tractor). Even still, a quality muffler will reduce drone to some extent.
I do have *some* experience with LS Swapped GMT400's believe it or not, but until you really start building it, my recommendations are merely based on fundamental basics.
Y-pipe, X-pipe, H-pipe. Everyone has an opinion and there are pros/cons to each. You going for max power or the best sound? When you choose headers and decide single exit or dual exit then start thinking about your intermediate piping.
Appreciate the info! Thanks!
I'm an old fart. Had carb'd BBc's with high lift/short duration solid cams, headers & 'turbo' mufflers. I don't mind noise! But, purposeful noise. The purpose was always horsepower, first & foremost! Lol!
The resonator was to kill the drone. Like I said. I don't mind noise, but that was just too much!
Yea, you're right in the ballpark for intended H.P. levels! 450 will be so much better than the anemic 160 the 250,000 mile 4.3 was maybe making. Backed up with the 3.73/Eaton posi now in it, this is gonna be stupid fun!
So, the purpose is to make power. Had vehicles in the past with 'H' pipes. Always impressed with the 'seat-of-the-pants' improvement, along with the better idle sound they provided. Was thinking of an "X' this time, although I was wondering about ground clearances as the truck is pretty low. Header-ground clearance has crossed my mind because of that, too.
Must...do...more...research!
Again, thanks for the info. Will probably be in contact when it comes down to the exhaust portion of this adventure.