Redmine

I'd like to install the better Gantt chart for 2.* on the current Redmine 2.3.3.stable system but when I check the available gems I get the error:
Could not find gem 'rspec (~> 2.10.01) ruby' in the gems available on this machine.

I have created rspec-2.14.1 along with three other rspec and one diff gem using the command:
gem install rspec

However, when I restart the server and refresh the browser for Redmine I get an error for an unidentified method (don't remember the exact browser message). So it looks like a version conflict between Redmine and the plugin at this point.

Has anyone installed the better Gantt chart plugin into 2.3.3, and are there any steps beyond creating the missing gems (RedCloth, sqlite3, rspec, etc.) that I need to know about? I'm an absolute noob at Ruby, by the way.

Thanks.