Hey jerozilla. Regarding the bars, I did try to slip them onto the steerer tube but found that I had to use a lot of force, either because the clamp is too small or the steerer tube is slightly oversized. I only got about 10-15mm before giving up. (I was just playing around anyway.)
I'll investigate further but has anyone else seen this? What's the recommended fix?
You should complain to the seller, either of the bars, or the frame. You can use a vernier caliper (it's cheap) to figure out which of the steerer & stem is the wrong size. Or use another stem. If stem B fits, then stem A is the problem, and if neither fits, then steerer is the problem.
You should complain, but sandpaper is the answer. ideally you'd find some decent diameter rod, wrap sandpaper around it, and sand down (i assume it's the stem that's too tight). You did undo the stem bolts, yeah?
i wouldnt be afraid of sanding that, because if you were able to fit 10 or 15mm, it means you really dont have much material to remove. Do wear a (good) mask, or do it outside, and / or do wet sanding, as that dust is apparently truly, truly bad for your lungs (when i cut steerers I use a water spray bottle so the dust doesnt fly off, then i wipe the black mud off the floor).
If it's the steerer that's out of spec, i'd be less happy, because it raises more questions, given how critical that part of the bike is.