Well... not in a Webley.
Factory .45ACP produces pressures similar to the .455 Webley proof shot. It's a bad idea to keep on running such ammo through your scarce 110-year-old gat. To own a Webley is to reload for that Webley, pretty much, whether the cylinder is shaved or not. .455 factory ammo is very rare at all times.
The rest of your post is spot-on. I too think the OP is being unreasonably obtuse with almost all his ideas, but he's dead set on .45GYAT. So that's what he's going to get. Far be it from me to dissuade anybody.
So long as he shoots safely and doesn't ruin a fine Webley specimen!
I started thinking of 45 in general when I typed that.