Looks like a 6.0 is around $1500. I think we will stick with the 5.3 and turbo it down the road. That being said what cam and springs do y'all recommend and what's a good company to buy from that will be able to answer any questions, not just a parts seller.
I know for a fact that the only difference between the 4.8 and 5.3 is the bore, a 4.8L can be taken all the way to 5.7, so can the 5.3L, creating an iron block vette motor, only it's capable of withstanding more boost than the aluminum block...:thumb: and then I think most if not all the LS1/LS2 stuff will work for the build.
Like I said, the bore is the defining element for the amount of displacement between the 4.8/5.3 they use the same crank and rods...it's been a few years since I was playing around with LS stuff, but I'm pretty sure you can bolt on LS1 vette heads once the blocks been bored over and even use a LS1 Z06 cam, with the right tuning that will surpass your 400hp goals with ease.
Lunati and comp make some pretty trick cams for the LS stuff, weisco pistons, JE pistons, Arais, MAHLE, any one of them would suffice, up you can even run a stroker kit wit a full 4" throw iirc???
I saw mention of using the 243 heads, but iirc, the bore on the 243 heads is 4.125 and while they can be used with a 4.05 bore or somethin, you have to pay special attention to the quench, piston wall to valve clearance and CR cuz the volume of the 243 heads is like 63cc iirc, and the standard heads used for those engines was a 72cc combustion chamber, also I think the valve angle is different too, 23* vs 15* but I can't remember
also the cathedral port heads can be ported out to match the flow of the stock square port heads, and even more so than the stock square port heads move, AND cathedral port heads flow better down low, producing more tq down low, which is beneficial for a vehicle as heavy as a truck, usually this detrimental to the top end, but if you can afford to send the heads out to somewhere like T.E.A (total engine airflow) you won't be disappointed
something like the 225cc-245cc heads from them would be sweet
http://www.totalengineairflow.com/cnc-ported-cylinder-heads/gm/ls1ls2
Really, the sky is the limit! Build it for more than your current goals and go for it later with a turbo set up