I just watched your video. I noticed 2 things.
First, you need to get that front lever (1st-rev) up to the neutral position or the cross-over blade will never grab it. Follow the instructions in the FSM.
Second, that small screw near the firewall needs to be tightened down. It should not be moving back and forth in the slot. That is the adjustment to take up slop in the mechanism. The inner collar is rotated to adjust clearance. IIRC, my 64 had 2 slots with screws, yours may only have one. You seem to have a lot of clearance between the various parts.
I have to leave for awhile and get back to work on my 4 speed conversion. Good luck!
