can rearview mirror be removed from arm?

need to replace the rearview mirror in my '68 911L but having hard time locating the "break away" style that was exclusive to that year. partsheaven wants $150 for used one. ouch. can i remove mirror from arm and replace with mirror from later style(up to early 80s) porsche mirror? i have heard this can be done but can i wrench on the mirror enough to pop it out and insert new one? tia.