Swapping out the FMX for an AOD was one of the best things I did for my 69 Cat. I know there are many options regarding which transmission from a particular year of car/truck ect ect...... I wanted to do this transmission swap just the one time, so I took a bit more of the expensive route and bought a professionally built AOD from Lentech. I have their Street Terminator taking the options of a 2200 stall converter, a Wide Ratio gear set (tighter first and second gear) and Lokar transmission lever. It's a good AOD, reasonably straight forward installation and, so far, no issues.
There's lots more I could say about it all, however, more to the point of this thread.......I didn't buy a kit, just buying only what I needed as I was able to reuse the FMX spacer and flexplate. The shifter link I just fabricated......that's just part of the fun. 3/8 round stock mild steel from home depot, a basic tap and die set, 3/8 Heim female rod ends from your favorite auto shop, two jam nuts, a vice, a blow torch and a BFH. Bend up a coat hanger to map out what you need and you're good to go.