I believe all the e28/e24 260, 260/5, & perhaps the 265 will work. On one of them (I forget which one), the input shaft is shorter & won't work. There should be references to that on the web. You might find answers on some of the links at the bottom of this page:
http://www.nmia.com/~dgnrg/page_41.htm
My question is why do you want to swap trannies twice? How long is the rebuild going to take? Wouldn't a rental car be cheaper than buying a 2nd trans?