OK. It is the Starting Control Unit Safety Belt 61311357360. Not super easy to see in the pic b/c a bear mauled mine, but Gurt-Anlass-Steuergerat google translates to "Belt Occassion Control Unit" & shows up as #19 in diagram 72/7. http://www.bmwmobiletradition-online.com/bmw/showparts.do?model=7013&mospid=47811&btnr=72_0315&hg=72&fg=05
I’ll clarify. I have seen a number of 1973’s with these wheels. Realoem confirms that they were available in early 1973. I can’t technically confirm that they were an option, other than they were available and can be found on some ‘73’s. The Hoffman manuals list the aluminum FPS wheel options as generic “Magnesium Wheels”, so no help there. They have only been available in Europe, and possibly only on the e3. Definitely available on the late 1973 3.3L, but that is equivalent to a US 1974. I’ll dig up a brochure if possible.Interesting, I had only seen them on 74s. Do you have a source for the intro date?