My 54 is running a 62" mount to mount on both front and back but I'm running the straight axle on the front....235/70/15's on 7" rims with 4" back spacing on the front and 255/70/15's on 8" wide rims on the rear, also with 4" backspacing. Both front and rear sit centered in the wheel wells and the front has ample clearance (5/8") with the tie rods....both stock and upgraded.
I probably could have run a 3-1/2 to 3-5/8" backspacing with no inside bed and outside fender issues.
As Joe mentioned, folks are quick to sell you stuff you don't really need. The 3-1/2" rim is pretty common and most tire dealers who sell rims will let you try out a rim/tire combo. Eastwood also sells a $20.00 rim/tire fitment gauge that lets you dial in exactly what rim and tire combo will look right on your truck.
Dave
