Personally I think if you have a base model with factory metallic paint then it is most probably a Sandman. It doesn't make sense that metallic paint was not available on base model HQ, was available on base model HJ, wasn't available on base model HX, was available on early base model HZ and then not available on late base model HZ.

Jade green is a nice colour and even better with 19V trim. Your Sandman will be worth more if painted in it's original factory colour. I would paint it Jade green and put the white Sandman decals on it..... very cool. However it is your car so do whatever makes you happy.

While this is a Jade Green HX it looks pretty 70's to me..... especially as the photo was taken in the late 70's...