Regarding the GCC specs, it's a metaphor, some of the manufacturers ship their old engines and downgrade some of the interior/exterior cosmetics/ electronics to this side of the world and people think it's a GCC specs, just like with JDM cars. The only +ve thing about GCC specs is that you get a fire extinguisher, but you can buy one here for like 20 $.

Regarding your Tundra, you won't be able to listen to some of the radio stations because of the digital radio settings,but the speedometer comes in KM so you are safe :)

If you have the 5.7 L or the 4.7 L, these engines are already available in the local market, so no problem regarding their spare parts.