In 1965 I BELIEVE the wagons changed frames. What improvement were made, are they interchangeable? Is one safer compared to the other?
To the best of my knowledge, 1964 brought the introduction of the next generation of a-body wagons. Frames remained the same through 1967. Sportwagons rode on longer frames. Full size wagons were discontinued after 1964, hence there were no full size '65-'69 wagons.
64 and 65 Sport Wagons have a boxed frame, longer wheelbase than the Special which is same length as the sedans, not boxed. 64,5,6,7 should be similar. The big 63, 64 wagons were on the X frame. I was thinking the earlier A body were unit bodies but I have not studied them at all.
small (skylark) adding to what you said. 61-63 were unibody cars with no frame. 64 has its own, shorter upper control arms, 65-72 are interchangeable and everything but that upper arm is interchangeable on the 64. The bushings on the lower, front arms are different - so beware if you're just doing new bushings - however, the bolt size, and bushing dimension allows interchange with the later stuff.... 66 the track width is 1/2" wider (flange to flange) but all of the arms and such, including the rear axle, bolt in from 64-72. Steering boxes, I bolted a GNX steering box into my 64 - which adds a whole nother level of mods. big cars were X frame as you said (Invicta size)