There's also a barrel/link, right? Blowback tube-guns have had their endcaps come apart before (crummy homebuilds) and the results aren't near as cataclysmic as you describe, so long as the shooter is using proper eye protection. It's more embarrassing to get socked in the mouth by the gun than anything.
I'm more curious how the slide is being arrested; is it just going to be hammering on the brass tube down there? If it is brazed/soldered into place in the slide, the connection should be plenty strong, but I would still wonder about peening. I also question the lack of trigger guard adjacent to the expose guide rod & slide nose, but I guess that's what gloves are for (and thimbles
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Is that one of the Sarco "80%" castings? Yeah, those things are nowhere near any state of completion. I'm digging the look, very "Golden Gun-ey" if you don't fancy it up much beyond the brass bits. Depending on how you do some engraving and finish work, you could go Art Deco or Victorian-ish with it, I think. Steam punk is hard to do with something as polished as a 1911, simply because it has clean & graceful lines (a Tokarev could pull it off easier), and it's not like you'd want to ruin those any way.
BTW, if your holes are in the wrong spot, it may be worth having a buddy TIG/MIG them up for you, and using an endmill in a rigid machine to reposition it. So long as you haven't done much else below the rails, I would think you can get as many do-overs as you need to square it in the jig properly.
TCB