What drive shaft

The driveshaft out of my '71 Dart GT with 318/904 and 8 3/4" rear is 52" even C-C. Should be the same for a 340/4 speed 8 3/4. Mine has 4260 joints, might be a little different going to 4290, but not much. Always best to measure, there are definitely factory tolerances to consider, not to mention ride height etc that play into that measurement.