I do not see it either. (I confess, I had to look it up on the Finale web site to find out what it did, as I have never used it.) Would setting up a region in the Edit Measure Number Regions do the same thing? Granted, this may take a few more steps.

You could always make a Feature Request at https://makemusic.zendesk.com/hc/en-us/community/topics/200449177-Finale-Feature-Requests?sort_by=recent_activity for MM to add a 64-bit version back into the program.

Also, have you checked out Jari's 64-bit beta plug-in's at the bottom of 

http://finaletips.nu/index.php/download/category/43-64-bit-windows-plug-ins 

I'm missing this easy-measure-number-plugin too! I sincerely hope we'll get it back soon.