Any rear mower bigger than about 60 in. will be heavy for a BX. So I'm wondering what advantage would be gained removing the 54" deck and replacing it with a 60" rear mower. The added 6" cutting width hardly seems worth the trouble, and you end up with something that's less maneuverable as well. Here's a thought... if you need to improve your productivity, for not a whole bunch more money you could get an offset pull-behind (Swisher, etc.) and mow 96" or more on each pass.