Although there is no video, that I am aware of, which illustrates the interlock problem of the ⅔ gear change there is a good video on 3550 / TKO assembly / disassembly done by Paul Cangialosi. At the 27:00 minute point in the video Paul gives a pretty good description of the TKO synchronizer problem. As he points out the TKO synchro's are essentially 1960's Top Loader synchros being asked to do a job they were never designed to do.
Check out the video it's quite good and if you have never done a manual transmission before or are contemplating servicing your TKO this is a great primer for you. Even if you are not it is a pretty graphic demonstration of the synchronizer problem. The whole video is a whisker over an hour long, the synchro story begins at the 27 minute mark.
Click here =>
TKO Disassembly / Assembly Vid
Ed