These are from a 633CSi built in 10/84. Note that they have a very sturdy ribbing in the back which seems to lend itself to cutting only as much as necessary.
Link to another faqer who did this conversion with this model of seats. Look down about half way.
http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,307348/highlight,e24/
More pics as requested:
Thanks for looking!