4"to 41/2 what backing plates
A visual on what the issue is...
Small bolt pattern A-body axles have a different flange offset than the big bolt pattern axles. So the backing plates for SBP axles also have a different offset than the BBP backing plates.
If you use re-drilled axles, you must re-drill your drums. This is also true for some aftermarket axles that have the BBP but have the SBP axle flange offset.
A visual on what the issue is...
Small bolt pattern A-body axles have a different flange offset than the big bolt pattern axles. So the backing plates for SBP axles also have a different offset than the BBP backing plates.
If you use re-drilled axles, you must re-drill your drums. This is also true for some aftermarket axles that have the BBP but have the SBP axle flange offset.