If you have drum brakes, you do need to take the rear axle portals off to get at the slave cylinders.. They are inside the drum, which has to come off the halfshaft before you can reach them.
I think you're either talking about the master cylinders, or about the slave cylinders of disk brake systems. (in either case i cant see why you would want to remove the cab floor)
A 5 year old 6341 has disk brakes... dont know if its the dry disk with cylinders accessible from the back of the tractor, or the wet disks found on current series. I dont know where the slave cylinders are located on the wet disks.