what is proper d.s length for 70 340 4-speed?

My 67 dart convertible, 4 speed & 8 3/4 has a 53" drive shaft (think that was to centerline of universals) . I think the 67 & 70 has the same wheel base. The hardtop/convertible has a longer wheelbase than a post car.

I also think the duster has a 108" wheelbase and dart is 111"

My 2 cents and it might not be worth a dime