The record with the 750s was set in 75, it was FIM,AMA, and SCTA.
In 79 or 80 the 1650 class was added for the HDs and It should have been reassigned to that I'll bet.
The worst part is the 318 Kawasaki record is gone from the AMA printing for the last 2 years and it has never been broken. The same problem exists with Corbin (elec) and Campos(2HD).
A lifes work gets very little attention when it is gone and less to restore it.