IMO, You would be much better off buying your wheels first and then narrow the rear to fit the wheels. 54" sounds too narrow, my rear is 57". My wheels are 18x12 with 5.75"bs if I remember correctly.
__________________ Steve Hayes
"Dust Off"
68 Camaro
Speed has never killed anyone. Suddenly becoming stationary, that's what gets you! "Jeremy Clarkson"