Exhaust help/suggestions needed

i just recently bought an OBX Type R catback for my 98 z24 5speed. I go to bolt it on and i ran into a little snag... all the bends match up but the catback came with a 2 bolt flange gasket and my stock cat has a 3 bolt flange. i wanna replace the stock cat with a hi flow one and get a header too... what kind of cat should i get and where do i find them at.... well header too... i wanna limit the fab i have to do but i need to find a 2 bolt flange cat but i dont know where to look. I dont know what size my obx catback is bc its in my friends garage waiting for me to put on. but i could use some help with all this... suggestions welcome...