Everything I've read say the only differences between a 46 and a 48 Mopar is the date on the title. The demand for new cars after WWII was so high, anything the car companies put out sold. There was differences in trim because the supply was limited and they changed as the available supply changed.

Dakota rear axles work well, as do B body 8 3/4. If you not concerned about fender clearance, nearly any rear axle will fit, these cars are pretty wide with a factory tread width of about 60". Gene