Jeff:
I think you're right. The later models do give just a little more room. The 3" you mention on the post 66 models; a little extra from the longer seat track -- maybe?; but also there seems to be some modification in the center console area (trim wheel etc) on the 1970s models resulting in a little more room for the knees too. My preference is for an L or M model, but I wouldn't turn down a nice G model forward.
Once a person is in, however, flying solo in any of the models seems about the same to me.
Don
