back in the late 70' and on, many folks ran 265-50 fronts and 275-50 rear with BFG radials.
i currently run 275-50 BFG drag radials on the back with 245-
60 on the front.
the tire diameters are virtually the same so it looks proportional front to rear.
1973 SD455 T/A
1979 SE400 T/A
http://community.webshots.com/album/16587603rOyvmFCiHs