There are rules, and then what is inspected.
California, cars 1975 and earlier don't get biannual smog check (I don't know about when transferred.)
Diesel, only OBD-II gets tested. My 1995 pickup predates that.
Engine swaps for vehicles have to be same or newer, and same class (can't put car engine in trucks, although in pickup is probably fine.)
Probably 1960 pickup, you could get away with anything.
Heavy trucks, older ones banned from the road. Only newer engines would bring them back.
(EV and a plugged in range extender might slip by until it became popular.)
The truck in question was in Canada? What rules there?