The oroginal fctory fit was roun mirrors on the 175/200/350 and the late model 100TMX. The 50s, 60s 90s , 100Sport, 100GP 100Trail and erly 100TMX all used rectangular mirrors. The deciding factor was handlebar diameter - rectngular mirriors for 19mm bars, round mirrors fit 22mm bars.
The round mirrors are larger in area and come with longer stems.
Hope that helps,
Graham