I would do 235/60R15 up front and 325/50R15 out back. That will give you a bit of rake and the 325's fill up the wheel wells nicely on these 71+ b-bodies. If you've done a mini tub they will fit, however I would expect custom backspacing rims to be needed. The 325/50/15's are a 28" diameter tire. Nitto and BFG have drag radials in this size. For more of a street tire, Mickey Thompson makes their sportsman s/r in 28x12.00-15 which is a little narrower and in terms of construction I think they are a street radial not a drag radial.