I beat the bushes for the source code, documenting my finds (https://mcjones.org/dustydecks/archives/category/lisp/) and posting them (https://www.softwarepreservation.org/projects/LISP/lisp15_fa...), but the early work was done by Jack Harper, Pascal Bourguignon, Rich Cornwell and Bob Abeles, Andru Luvisi, Angelo Papenhoff, Al Kossow, and others.