Man you dont want 31" tires IMO it will look stupid, you only want a 285 width so go with something like 29" tall and 27" up front because 31" tire to a 27" tire is way too staggered for a r/t, unless you have a full tub on the thing. Not to mention a 31" tire would make ur gear ratio go from 3.92 to about a 3.20 gear because its 3" taller than the stock tire and your speedo will be fast by like 8 mph

 

if u want to do a combo find some 30" tall mickey thompson rear tires and go with one of there sportmans front tires that are like 28" tall IMO that would look nice