'60s vs '70s Travelall 3rd seat

[PB Schechter <pb@domain.elided>]

Does any one happen to know whether a 3rd seat from a '70s Travelall
will fit a '60s Travelall?  I have the '60s one, and think that I
may have found a '72 seat for sale, but am not sure if it will fit.

As an aside: I assume that I would need the parts books from both
the pre-1969 and the post-1969 models to answer this question myself.
Is that right, or is there some other (mysterious/magical) way of
figuring this out?

Thanks in advance.

PB Schechter
pb@domain.elided