i've learnt from my time within the jap imports, that very very rarely have any history, the value of a good engine oil flush the moment they land in the workshop.
its an old idea, but the new products and the success i've had with them, convinces me that it is an effective way of keeping those all imprtnat galleriesand oil paths clear.
i flush every time now, its only about £6, but i do oil changes often and early too, preferring to have a reasonably priced proper basis protective oil, none of these liquid gold magnetic radiocative fairy liquids call oil!
i don't believe in having oils, plugs etc made of such exotica that they last 5 times as long, i'd much rather change it more often, which in oils case, help bring the dirt out of the engine anyway, as even the basic oils have suspension additives to keep the dirt in the oil, and not in the galleries, supposedly.
i wouldn't particuarly pay too much attention on "classic" engine designated oils either steve,
80's design or not, it was modern for its day in terms of tolerances and performance, and not many other engines of that era will rev like these beauties either, so i wouldn't consider it totally suitable,
in my own humble opinion of course.
apart from what you no doubt learn here, you could try a company called Opie Oils?
i have consulted with them on many occasions about far far higher stressed engines than ours, and various other applications and oils too, and have always found them accurate.