Spare tire and rim size for 70 Duster

Remember that the whole lower body section was designed back in the early 60's and the A-Body came with little 13 inch tires on narrow rims that fit the spare tire well.
Going up to a 14x 5.5 rim and tire sorta overflowed the well.

Check this link out and on the last picture where they are holding the cover up you can see that the top of the tire is higher than the trunk floor.
Of course in the picture that shows the mat down, they have very slyly removed the tire so the trunk floor and mat show to be flat.
Place a thin piece of Masonite of the same size placed under the cardboard will help a whole bunch in keeping the cardboard in good shape.

Courtesy Of The Hamtramck Historical Site:
http://www.hamtramck-historical.com...lershipDataBook/1971/71_Valiant_Duster_12.jpg