An accurate 8 3/4" rear axle width list
If dr. diff knows your plans he would have sent you axles with offset to match your backing plates.
Be aware your overall width drum to drum will be a little wider than a factory stock small bolt pattern abody 8 3/4.
If you're having your housing narrowed you can correct for that if you want to. If I remember correctly there was plenty of spline length on the axles so cutting them wasn't an issue.
I didn't correct when I did my drum rear because I already had an abody housing. I did on my rear disc brake rear end because it started as a b-body housing that was already being narrowed anyway.
Hope this makes sense.
I only bring this up because you are asking for wheel offsets for your dart. If the person you ask has a factory small bolt pattern 8 3/4" rear keep in mind your's will be a little wider than their's.
