An image of a British carrier fitted with the 2" mortar on the engine cover.
A drawing from the Canadian Army Modification Bulletin of the 2" mortar mounting assembly, part number CTL-739-SA with the modified firing rest CTL-1562-A.
Looking at minute 08:07:18, the modification installed on this MK-I* showing the firing rest being lowered:
https://youtu.be/01mNiOJhaX8
Compliments Richie post #24.