By the time you modify that 9.25 to work you might as well get a new Dana or a used 8.75. But, unless you can find an 8.75 that will fit (A or B), have a posi and have the right gears and brakes i'd go with a new dana.
My Dana from Strange is tricked to the 9's and was just over 3k delivered. The comparable 8.75 is about 5600 delivered.
A used 8.75, ready to go is worth about a grand but finding one in that condition is not always easy.
Good luck with the car. I've done 2 big block darts. They are impressive machines
