Hi Ron,
They are beauties. Peter Grecke was a well known gunsmith from Rostock, Germany during the mid 1700's. He eventually emigrated to Russia and worked at Tula. Are you sure the bust is of Maria Theresa? It certainly could be if the pistols were made before 1755 or so when Rostock was connected to the Austrian Holy Roman empire. However, if they were made after 1755, I doubt the image is of Maria Theresa because Rostock was occupied by the Prussians under Frederick the Great and at war with Austria. The bust actually looks a little like his unhappy princess, Elizabeth Christina.
Thanks for sharing,
Dave