Should decades (e.g. '70s) be singular or plural

Are specific decades singular or plural? Which of the following is grammatically correct?

The '70s was a great period for rock music.

or

The '70s were a great period for rock music.

Please provide references if you have any.

My interpretation would be this (including source).

Rule 8. Use a singular verb with distances, periods of time, sums of money, etc., when considered as a unit.

The '70s is a period of time

Examples: Three miles is too far to walk. Five years is the maximum sentence for that offense. Ten dollars is a high price to pay. BUT Ten dollars (i.e., dollar bills) were scattered on the floor.

Rule 8: Blue book of grammar and punctuation

My intuition is that it can work either way. If you use "were", then you are treating it as a collection of 10 years. If you use "was", then you are treating it as a single decade. This is similar to how teams and corporations can be singular or plural depending on how you look at them.

On ngrams we can see that both are in use, though the search result is misleading because there are false matches like "The X of the 70s was a good X".