Glad you made some progress Chuck!
Everyone says that Frank Timko is a wizard when it comes to removing and installing worm gears. Maybe he would entertain a phone call or chat, and offer you some advice? Honestly I wish someone would invest some quality time shadowing him, or even make a video. I think the worm gear swap will become a very important repair skill in the years ahead.
Also, if you really needed to use the 8060 motor from the baby 4-6-4, couldn't you just drill new holes in the mounting plate a little further apart, that match the 8060 motor? Thanks for sharing, we're all learning from your struggles!