John,

yes, MB in /conf/config.json

In v0.9:
I found "maxFileSize" at adapt_authoring/node_modules/formidable/lib/incoming_form.js, as mentioned above by Daniel. I increased it. AAT import manager's label still reported 200MB max. Attempted import of a file greater than that failed.

Then I found "maxFileUploadSize" in adapt_authoring/lib/configuration.js at line 84. I increased it. AAT import manager's label still reported 200MB max. Attempted import of a file greater than that failed.

Then I found "maxFileUploadSize" in adapt_authoring/conf/config.json. I increased it. AAT import manager's label now reported my limit. Attempted import of a file within that limit and it succeeded.

To satisfy my curiosity, I then reduced the max size only in /conf/config.json, and attempted to import a file greater than that limit. It failed. So I'm concluding that the only place that matters is in /conf/config,json.