Remember to shoe horn the 5.3 in the H3 they flared the front frame and moved the firewall back some, or so I heard from a reliable source. lol
Might want to do some serious measuring on that.
I did service work at the assembly plant where these were made in Louisiana and that is correct. There were some firewall mods but I'm not sure exactly what they were. I think it also had to do with exhaust clearance. Everything after 08 had the same sheet metal. V8 or I5.