I have two 45-70 H&Rs with Nikon Omega 3-9x40 scopes(5" eye relief) mounted in low Leupold PRW rings which are .230" from the top of the scope rail to the bottom of the scope tube, indentical in height to medium Burris zee rings , both have shortened hammer spurs for clearance. The Prostaff has less eye relief than the Omega, so you'll have to mount the scope further to the rear, so you may not have to trim the hammer with mediums, only way to find out is to try, see the FAQs for info on low profile hammer mods.
Tim