Here's my advice for anyone having similar problems:
First of all, run through the drop script line by line, and make sure you understand what is happening with each line. I found that parties were dropped anyway -- I didn't need to explicitly do so.
I also found that in the first inline function, I typed organizations instead of organization, so the objects weren't being deleted. This is what prevented the acs_object_type__drop_type portion of the script from working.
The drop script now works.