If you are going to get it cut, let the smith recrown. I would think there's a way to crown as you cut- turn it on a lathe and have the cutting bit at the right angle for the crown. A glass marble with polishing compound can finish it off.
And 1/2-28 UNEF isn't .500 OD, it should be 0.4989 to 0.4924 for OD threads and 0.460 to 0.469 i believe for ID threads for a major/min diameter... for 2A/2B threads.
As far as the length, that's up the suppressor manufactuer and they should match the required length and the suppressor should bottom out on the machined surface. There's not really a spec to length for 2B.
It's very important that it bottoms out against the barrel, however, or the suppressor could be basically sitting on there crooked even if it doesn't look like it, and that in itself will cause a baffle strike.
The threads themselves look reasonably nice, i'm not sure what I see on them, it might be dust or lint but if there is little nicks on the threads then they didn't use a new threading insert or they used a high speed steel threading tool.
You should probably get a spanner wrench and examine everything before buying a new baffle, because you'll need the wrench anyways.