Also (I am assuming you didn't get any original docs with it)
But try prior owner history, see if you can talk to some prior owners, and maybe they might have pictures or know someone else who knows the car.
As far as advice goes, before you start gathering Z parts (which are expensive), I would research as much as you can on how the car may have come originally. If it has the original trans with the vin stamped in it, that would be a good first step. Maybe you get lucky and it ends up being a Canadian car and with that it would prove it originally was a Z.
Find out about the trans, and lets see some pics of it then and now please