So far so good. This worked for me. The unit rebooted after I put the NN746UC image on. Then testmode would reboot and reboot. I reinstalled the wince files in service mode and transferred the files over in testmode. I have the unit on bench power now, I'll play with it tomorrow to make sure all is well.
Thanks for this writeup, it really helped!
BTW, this is on a 700BT. I'm almost doing flips!