3.31 to 3.73 worth it?

3.73 is a good ratio for your application,3.91 would be a bit too much. The swap is well worth it, you will notice a difference...Years ago i owned a 70 dart 340 w/4 speed and a3.23 open rear,,, What a dog!! Installed a new center section w/ 3.91 and sure-grip,, it felt like it had a 440 in it.....