I made this exact swap on our '66 Carryover. I believe the shifter control box is the same for both the top-loader and our T-10s. The linkage is different The tabs that connect the linkage to the transmission are different also. The tabs for the top-loader are rectangular. The tabs for the T-10 are oval or egg shaped as you can see in the excellent pictures posted by GJZ. I found my shifter on Craigslist but you might also put a "wanted" ad here on the SAAC Forum and the Concourse Mustang Forum. The prices seem to range from $300 up to $600+ depending on condition and what parts are included. Getting the shifter handle and knob is a bonus. Plan on rebuilding the shifter. Scott Drake sells a nice kit.
Jeff
Jeff