can a 02 motor be in a pre 99 truck?

[myredtruck]

hey i just started my headgaskets and as i cleaned off the valve cover the passenger side says its a 02 motor? the drivers has a 01june 01 sticker. and the turbo is a 1.00 that looks alot like a late 99 we had.
So did they put a newer motor in or is it just got new valve covers? and if they did is that going to mess with my electrical for chips and things?

next question , to yank the passeger head do i need to remove that heater box? cus im not sure i want to but might have to. thanks guys!