Just had a big WTF?! when I found this Scuderia Nissan ad from 1971 on some historical Skyline GT-R KPGC10 related site:
Scuderia Nissan ad from 1971
Scuderia Nissan ad from 1971

Basically it offers to transform your road legal Skyline GT-R to a racing spec car.

Found at [Spirit of Skyline]