early A - later A interchange

hey all,
i've had my 64 dart for about a year and done a complete driveline swap from motor to rear end and done a lot of other small stuff too just in the process of getting it on the road and reliable for daily driving. this is only my second project car and first mopar and i kinda jumped in with both feet and no lifejacket. its gone very well so far, i've done everything on my own with the only help being with the heavy lifting and the real critical technical stuff.

my question to pose to you guys is this: what kind of interchange is there among the first and second and third generation a-bodies? seems like 66 was a transitional year so i'm wondering what 67+ parts can be made to fit in my 64? driveline and chassis upgrades (i know about the disk brake swap but curious about other stuff)? i've already installed a '70 8.75" since i broke the spider gears in the old 7.25". seems like the later cars are a lot wider but how can that be if the rear ends are the same width. shouldn't the chassis be dimensionally the same width then?

what about dodge/plymouth interchange? for instance, would a 64 valiant dash cluster bolt into my 64 dart? trim? windshields? door panels? etc etc etc.....

anyway just throwing this out there to you guys as an a-body newbie looking to increase my knowledge base, so fire away!!!!

thanks!!!

-tim