Most stuff on the internet about the coffins is guff. It's a library job I'm afraid.
Scotsman 18th July 1836 for original report.
Other mentions from the Scotsman are 16th May 1906
Evening Dispatch 16th October 1956. (this is mince-sounds almost totally made up)
Book of the Old Edinburgh Club Vol 3 1994 Menefee and Simpson West Port Murders and the Miniature Coffins from Arthurs Seat-the Burke and Hare Theory.
If you want to know anything I can tell you.
Edit-wrong year on a reference, d'oh