anyone who puts a carb on one of these engines is retarded. properly tuned fuel injection will make a carb'd engine look like a gen 1 POS in any condition. it's people who dont know any better that put carbs on them and think they are doing some good.
if you want a lot of potential then go with the 6.0L, if you want up to 400hp then a 5.3L is a good choice. a cam that sounds cool at idle is bad for low end performance. if he were to put an adjustable cam gear on it he could advance it and get some of the low end back but he's already screwed it up with that carb.
I have a 6.2L L92 and I turned it into an LS3 be removing the cam phasing. I did some research and for a couple dollars more I can put the cam phasing back on and get more low end and top end than a fixed cam. a fixed cam engine takes the low end torque and turns that into horsepower on top when you put in an aggressive cam, a stock cam will keep the low end but you lose your peak HP numbers and get a flatter power curve. Needles to say I'm swapping to VVT and going with an aftermarket cam. 530hp with more torque on the bottom end than a stock engine.
the truck intake flows better than the car intake, keep it on if you can and dont go too crazy with a cam, less is more when you arent operating in a 1000 rpm window.