Hello Stevea,
The first stage of identifying a US FJ40 is a look at the front wing (fender) mounted indicators - for the US they were round with yellow (amber) lenses as opposed to the square split side light/indicator version. But that does not completely confirm that the truck was originally designated for the US market as some other regions also had those indicators but is a good starting point.
Secondly you would need to see the VIN plate: For the years applicable to your search there are only two id tags -
1. FJ40L- KJA
2. FJ40LV-KCJA
Both had 2F engines -4200cc, 4 speed gearboxes and roll bar.
Trucks destined for Canada and C/American had different IDs. For '76 though '80 these are the only tags applicable to the US market and everything else is an import.
Hope that helps and good luck with your search.
regards,
Rodger