I could be wrong but my chart shows 1978 started with srn 1001 and 1979 started with 1501. So I don't think have the first one, but you got an early one. I have n7 1281 and 1350 and n6 1783 in our salvage yard.
the first N6 was sold after the R2 series was introduced if my memory serves me well. It was a preproduction model and was used for testing up to the 80's. Don't know the SN but know that it was the first of 2 post prototype - preproduction machines and was used in field days for comparison . It was then retailed somewhere as we tried to sell it but didn't get the job done.