You'd need a bellhousing, crossmember/mount, shorter driveshaft, and some other odds and ends. I say it depends on just how 'cheap' you can get that tranny. The stock 10 spline input shafts on 03-04 Cobra T56s aren't so great. You can get a 26 spline from someone like Liberty gear. They're about $200-250 IIRC. You could always upgrade 5th and 6th gear to Viper spec too if you wanted. Keep in mind T56s are much heavier than your T5 too, if weight concerns you.
+1 to what sage2k said about little things adding up. This TKO swap is never ending.