The new front sight is installed.
Slide as was:
I tried something before going drastic, did some careful file work to give the back of the blade more of a square profile and painted it; still just too small. So back to the vise(padded, of course) and file. Slide with front sight filed flush:
Then used a prick punch to very carefully mark the center of the former front sight, to give the drill a solid place to start. And if you don't think starting that bit down was nervous time... Hole successfully drilled, time to tap the hole. I mentioned using the drill press for this, here's the setup:
I'd centered the spot to drill and then clamped the vise down so it couldn't shift, so just opened the chuck enough to remove the bit and insert the tap. Then, after a good dollop of cutting oil was applied, run the tap down to contact and then turn the chuck by hand, using just enough downward pressure to let the tap feed itself in as it cut. The press makes sure the tap starts and stays straight. Turn forward a bit, then back to clear chips, repeat until done.
Hole threaded, flush it out to get rid of any chips, clean up any burrs on the edges, then start fitting the sight. Had to(very carefully) lock the sight upside-down in a vise and file a small amount off the bottom to get the sight to turn far enough to line up; when done, clean the shank and hole, apply threadlocker and install.
That sucker glows very nicely in dim light. Yes, it'll probably throw the shots low compared to the original, but I'm going to try it out thoroughly to make sure the sight will stay solid before I start on a rear sight. As mentioned in the original post, if it doesn't, I'll dovetail the slide and install the new sights that way.
Dammit. I was going to recommend this tool if you do much tapping, but it's been discontinued. Dammit again. I'm having one of those "Why didn't I buy one back when?" moments.
Update: can't find the place/post that had the sight mod I remembered, but did find this; I'm going to have to find out what sights they used, they're perfect for this