have found the plate, its no Origanal, I think its a copy as its made of Ali or something like that but not brass.
It reads
No 6586
Carriage, How, 105mm
M2A2
Parish Pressed Steel Co
1953
Its not the sharpest casting but it is readable, if you painted it brass colour, or green like the gun it would look fine
I'll try and post pictures over the weekend, its for sale if your interested ???