Harold I am admiring from afar the work you have done on your TU.
I don't know what method you are using to actually solder the flatpack.
The 'easy' way is to place the package and tack solder two corner pins till it is where you want it.
Then flood one row of pins at a time with liquid flux
Drag a loaded soldering iron tip across the pins. You can do an entire row in about 5 seconds.
Metcal used to even make a special tip with a small solder reservoir in the end (i.e. a hole) for this purpose...
Regards
Gerry Block