Thanks, gents, for the suggestions. Keep 'em coming!
Found the manual online as a .pdf, printed her off and so there's Job One done:
Much excellent reading to be done there.
I've made contact with the Limber Gunner fellows in Toronto as well as Gilles Aube of 3BAM in Quebec who are all doing now what we want to do with our gun in time. They've been very helpful indeed.
Re: welding an addition onto the top of the shield - yeah, I'd like to keep the gun as original as possible. If that weld could be done in such a way as to be invisible, that'd do nicely. My only concern is that there's a hinged piece up there that might be hard to reproduce. Bears more research. Does anyone know of a set of blueprints, or very accurate dimensional drawings we could work from?
Question to the current owner/operators of a 25 pr. Mark II - any trick to getting the striker block out of the breech block? Near as I can tell from the manual, one pulls out the catch and rotates the striker block 1/6th of a turn clockwise, then slides it out back. I can't help but think that if it was that easy, some chimp would have taken it years ago when she was parked outside accumulating that lovely patina in the bore...
I'd like to get the striker block and breech block out of the gun and scrubbed free of paint, then relubed correctly and reinstalled. That'd be easy enough, and allows us to bring loose part home where they won't fall prey to sticky fingers.
Re: brass tags - I imagine these can be reproduced if we have a set to work from. Any ideas?
And yeah, that bore. As a lifelong shooter, looking down that cruddy old pipe makes me slightly tearful. Gotta get that shiny.