i see no one answered you. and i don't really know. i think the tan is different. tanning to be mounted comes back soft so it can stretch around the form. did you want the hair on for the garment or just leathered (hair off)? my hubby is the taxidermst but he is not around now. and he sends his hides out so he might not even know!
sorry you did not find your answer here. but you can check out the tanning forums on the taxidermy.net.
A garment tan is mountable. As stated above, make sure everything is turned and split for a lifesize. Also remember that the shelf life of a tanned skin to be mounted, is about 5 years.(three would be better) After that time you need to get it mounted or wet the skin up and freeze it, to be mounted later.