Heads & Cam

[HUMMERcustoms.com/TAZ]

MSeeb You would be good to go with the heads as long as You have the forced induction like shipbldr says. The purpose of the head is to flow that extra air your forcing through. Free flowing air at beginning, middle and end makes HP.
I'm going with a set of heads from LPE. They have a set that they do not advertise for sell that if You will ask they will put You onto them. I have visited with them about LS6 heads and they said a waste of money and disappointment awaited Me.
I'm thinking about 5.18 rear gears also to get more low end with all the other changes just as shipbldr explained. So unfortunately if you start messing with anything more than just 5 or 6 lbs. of boost to get more Hp You start needing to spend more money and fuel economy goes down more. Since I do not use mine as a daily driver i do not care how much it burns. But, the next one i can bet I go with a turbo most likley a twin turbo to use for daily driver and drive the Mall Queen less.
So you have the right idea and depending on Your boost You could get from 40 to 100 HP like KenP says. You would have to run allot higher boost to get the higher number.
I'm running 12 lbs. and is why I began to look into head change. But, then You get back to how much is the stock block going to take. Ken has the mods in His engine to take almost anything you can throw at it. So heads will be alright if Your are tame. To get the higher HP in mine at 12 boost could damage something. So the way around that is to cool air intake down with water/meth inj. along with CO2 spray on aftercooler and cool fuel down with ice bucket on the occasion You run it real hard. Plus get all the heat out of the engine compartment you can. Run an extra oil and tranny cooler with a fan. Anything that reduces temps is helping.
For each one of those first 3 items You can reduce the effect of detonation by 2 lbs. of boost aprox.
So you would get the HP and torgue, like You are running only 6 boost at 12 and limit damage. Someone is more likely able to explain it better than i did but, it makes it safer to run high boost to get high torque and high HP.

TAZ