Having watched just about all of the All-Japan archive in the past few months, and other Tsuruta matches where I have found them elsewhere, I can vouch for the quality of Jumbo's matches in the 70s, including '76.
It's not absurd to nominate that year; nor do I think many people would overlook Jumbo's '91. If you can nominate two years from a wrestler that are 15 years apart, I would advance the proposition that Tsuruta's standing in the recent GWE falls a bit short of what it should have been.