I haven't measured mine but I have a late 70's Disk brake Camaro/Firebird rear end going under the 48.
It has a mid 70's Nova rearend under it now and with the 255-60-15 tires on 8.5 rims I barely have any clearance on the inside of the tires to the sides of the bed.
This time around I am going with a narrower tire and wheel combination but will still need the offset to clear the bed sides.
A ten or 12 bolt out of a late 60's Impala fits real well but you have to clean a lot of scabs off it when you change it over for different suspension. Most guys wouldn't want to run one because they have a ton of brackets welded on them that have to be cleaned off. The 48 had a 66 Impala 12 bolt under it with 14 x 8.5 Crager Mach 8 rims and N-50 tires when this photos was taken and the N-50's fit the wheel wells pretty nicely.
