This is the package you're referencing? The $4,500 is machine work/time of your heads for the guides being replaces, parts, and installation pricing with 3yr/36k mi warranty included.
https://store.katechengines.com/ls7-...kage-p732.aspx
Are you looking to do the work yourself (having the skill set to do so) or have a shop do it? That's the question if the pricing as 'extremely high' as you put it.
There are no aftermarket heads that could just be bolted-on without tuning. All aftermarket heads are performance upgrades or at least variation from the stock units. Tuning would be needed at least. Plus all the miscellaneous parts that needed and assembled with the heads.
If the list you end is what want then this may be your best bet if you're shopping Katech. Again, parts and installation pricing with 3yr/36k mi warranty included.
https://store.katechengines.com/stag...kage-p685.aspx
Shops were recently discussed here too:
https://www.camaro5.com/forums/showthread.php?t=553991