In all honesty I wouldnt waste my time. 6061 isnt going to stop heatsoak into the intake plenum, and on any modern engine things like spacers for the throttle body or intake manifold dont serve the same purpose they were originally designed for. I am not trying to say the guys with the page you linked to lied, but more than likely took the worst dyno from the truck before the install and put it up against the best dyno after the install.
On older vehicles that were either carbed or had fuel injection to took place either in the intake or in the intake manifold these things served a purpose because they lengthen the intake and increase the swirling turbulence in the intake. They gave the fuel more time to mix with the air that was available and atomize and actually served a purpose. On our more modern engines the fuel is just injected too close to the combustion chamber for them to really make much difference. That and each port has its own injector so there is no need for mixing the air and fuel going into the plenum.
If you really want to do it just for the heck of doing it, I say go for it and see if it helps. I would imagine at best you would get slightly better atomization of the fuel going into the chamber which may let you run a bit more advanced timing which would improve you torque numbers a bit. You would probably be better served by giving the fuel system a good cleaning particularly the fuel injectors. God knows I am constantly doing stuff to my project cars that really makes no sense, but I get bored.
Apply dirt liberally, rinse and repeat
<<<-click for build
cut a bit
Lifted it more
welded a lot
cut some more
Got a winch
Parked until I can get a new steering setup.