Thank you for these generic responses.
As noted above, I have already run the Sucuri and unmaskparasites scans, both of which came back clean.
The ottopress article tells me what hacked code looks like, but doesn't tell me how to resolve the problem.
The wordpress articles tell me to do pretty much everything I listed above as having done already, aside from a complete deletion and rebuild of the site. So, by eliminating everything I've already done, am I to surmise that the latter is the suggested solution?
And Questas, I've seen you recommend that plugin in several threads. It's not going to solve a problem that already exists, but I will look into it to prevent further problems.