My duster has a 4 speed trans tunnel and I need one for an automatic. Does anyone know if there is a difference in the trans tunnel for a '70 and up dart, duster , valiant. Valiants and darts are more plentiful around here than dusters.

Any '67-76 A-body floor pan will work.
Just drill the spot welds to remove the 4spd hump from your floor. Use a piece of heavy kraft paper to trace the opening and creat a pattern. Be generous and add at least an inch all the way around. Trace the pattern onto the floor of the donor vehicle and start cutting.
Trim it down to about 3/4" overlap, drill holes centered on the overlap about every 1-1/2" to 2" and use a mig to spotweld the patch panel back in. Don't forget to use seam sealer to finish the job.
Mike

Thanks for the info.