If you open Font Book and click the disclosure triangle beside Arial to open it, you'll see two sets of each font. Then use Get Info (Command-I) to see the version numbers listed for each. If you deactivate all of the Version 2.90 fonts under Arial (Bold, Bold Italic, Italic, Regular) then any new page you create will show up as text (the old pages will complain of not having ArialMS, etc.).
I haven't figure out how to make a document that was created using the 2.90 fonts work with the 2.60 fonts, but I wanted to post this here so a solution to that last part can be found.

