All I did was call MM, told them I wanted rear H&R super sports for an 03 cobra vert with IRS, and that's what they sold me. Same with Steeda, no idea what part #s were sorry. Oh one thing Steeda asked me was the spring rates the H&Rs had, that way they could set me up with a similar rate for the front. The H&Rs had a 680lb rate, so steeda got me 650s for the rear.