hehe nahh not "3"
the right spindle bracket may (or may not.. depends on it's age) have a serial number stamped in,
but IIRC that was later (1982++ so sorry for misleading info earlier)
look for a plate pop riveted to the floor pan (under the seat)
If that's not there
the last option is the front side of the seat mount tab.
And if there is no serial number that still doesn't mean anything yet
(since I'm still convinvced it's a Xpert II or maybe an Xpert (I) but a Margay for sure

)
but you'll have to send some pictures of your kart
(first two, sixth and eighth of post #10 for example)
to margay... technical[at]margay[dot]com
they will tell you exactly what it is.
'sid