1970 Dart 340 / 4-speed driveshaft question

ok first off can anyone tell me what the correct length of driveshaft is needed for my car (center to center) of u joint? The driveshaft i have is 49 3/8" center to center, when installed in the car the engagement of the splines is roughlt .100-.125" of an inch, so basically no engagement just kind of dangling there. The slip yoke is machined for the first 1.420" before the splines start. Is there a slip yoke with splines all the way out? The car is all stock, stock 8 3/4, stock a833 4 speed, everything is in stock location, no modifications? Thanks for your time.

52 5/8"