Symmons 301 Nu-Arm shower head replacement with Symmons Dia retrofit shower column

Waher

Anyone have the odds or advice on replacing a 1990s Symmons 301 Nu-Arm connected to 1950s threaded brass with a Symmons Dia retrofit shower column https://www.symmons.com/download_asset/?id=35EX_Installation_Guide without having to tear open the wall to deal with crumpled brass or a snapped off elbow? Best case scenario I think I will be able to unscrew everything with a 12" spud wrench and a 8" Stillson wrench to put a new threaded brass
nipple into the original brass elbow in the wall to provide the 1/2" of 1/2" threaded pipe necessary to install the shower column. I don't think the original brass was replaced with soldered copper in the 1990s when the bathroom was last renovated, so it should still all threaded connections. I can't turn the head off by hand, so I'm worried the force necessary to rotate it on a 70 year old brass assembly may be more trouble than I'm prepared to deal with.