I see all kinds of posts about swapping out the front suspension with newer front ends with disc brakes and power steering but..................

What about upgrading the rear drivetrain on a 64 c10 short stepper?

We changed out the front from a 76 GMC. Now it has 5 lug wheels, discs and power steering but the back half is still 6 lugs with 3 73 gears.

What options should I consider?

Thanks in advance.