Actually 16 3/8" in the barrel*, now ready to try out.
In the spirit of 'screw with what'll cost the least to replace', the fitting was done on the front sight, not the dovetail in the barrel. Bit of an odd size, all cutters were either a bit too large or too small. Used the closest 'little small' size, then filed the base of the sight till would slip partway in, made sure wouldn't be too tight, then used a brass punch to tap it to center.
Also, as the magazine tube caused a fair bit of downward tension on the barrel when the front band was installed, VERY carefully put a slight bend in the tube so it would slip on nicely. Probably not necessary, but I feel better.
Added: on this mag tube reshaping, when I got to the range I'd expected I'd have to either raise the rear sight or file down the front, since the front sight- now being mounted on a thicker portion of barrel- would be taller. Instead, it was hitting high. REAL high, as in ~5" high at 30 yards. Apparently that downward tension on the barrel had been affecting POI previously a lot more than I thought.
Only 'Aw CRAP!' moment was at the very end: the end of the lever fits into the bolt, a pin locks them together, and there's a screw that goes on the left side of the receiver that locks it in place. Said screw was not to be found. Lesson learned a long time ago: take some masking tape and use it to hold group parts(like lever, pin, screw) together. Lesson reminded of today: check the damn tape before it goes in the trash can, it's easier on the nerves.
Now for time to get to the range with a box of ammo.
*I would far rather find it a touch longer than shorter.
And yes, I CAN twirl it. Part of the function-testing, y'know.