Can you help identify this aircraft cockpit part (most probably RCAF)

Good day,

Received the below photos from a small Canadian museum to whom this gunsight mounting bracket and Mk. IIL sight were recently donated. Asked for my help to try to find to which aircraft it was originally fitted to but I’m at a loss with this one. first thought P-40 but that bracket is not like anything I’ve seen before.

Here is what we have:
– Assumed RCAF. A/C 340 written on the bracket long ago
– The following part numbers are on the bracket: 68006, 68007, G31619 or G51619
– definitely for a Mk. II sight but not sure the Mk. IIL is original to this bracket

Looked at the list of British and US part numbers that can be found on the website but correspond to nothing.

Any help or idea really appreciated.

cordially,

Laurent