Not sure if it is ok for stock. Best bet would be to get a hold of a rule book. From what I remember, and personal experience, non- commercially available cars are not allowed in the spec (stock) classes.
At the 98 nats, my Dad got a first Gen Kawada SV-10 that I was going to run. Long story short, car broke so I did not end up using it, however we were made aware we would not be able to run in in stock, had we had the opportunity.