REAR DRUM STUCK IN TRANSMISSION

I've had a few do that. Realize you may be buying a few hard parts when things get married. Drilling the two holes in the back corners of the sun shell is a great idea. I've usually had success using a dead blow hitting the end of the input shaft sideways while turning the geartrain.
If you remove the whole rotating assembly it will still be one unit because the planetary snap ring is under the stuck rear drum.