This is the first -- special paint H/O L78 Nova I've ever personally seen. I know of one other on the East coast. I lived through the hey day of the muscle car years, and never saw one that was original. I think there were more -- special paint Novas done in firemist Caddy colors than H/O. I can think of at least three of those off hand. My semi educated guess on H/O L78 Novas would be somewhere around 70-- H/O Chevelles numbers. Maybe 10-20.
The Grossman connection I think is interesting as they were a Yenko network dealer, and also sold ZL1s. Where was yours sold new from?
Please post some pics of your car. I'd be very interested to see it.