If you want to keep your original transmission you need to find a closed tube from a 3/4 ton which only goes half way back,and open from there on back.You would have to have the back half shortened to fit,and the rear joint changed to fit the rearend.You would have to add a cross member to support the midshaft bearing,a piece of 2 inch channel will work for this.A rear from a 55-59 truck is ideal but a newer one with 6 lugs will do also.You will need to dismantled your rear springs and turn them around to keep the wheel aligned in the fender hole.

_____________
Floyd

If we choose being kind over being right,we will
be right every time.
Knowledge is a poor substitute for experience.
Remember what is precious to another, may not be to you, but it
is precious nonetheless.

1948 Chevy 2-Ton