hi mate,
i bought mine over 18months ago, and it had been out of rego for 4months pior to that.
i have just finished rebuilding it. though it is pretty much stock.
from what i have been told all i need is a greenslip, blueslip (which i have, and i think the blue cancels out the need for a pinkslip).
but if yours is to be heavily modified then you'll need engineers certs.
if you need them take it to paul irish aka sexy 16. he'll be able to sort you out.