Not sure if I understand all the issues you are having. I bought new e-brake cables for my 1952 and didn't have any issues. I recall having to first insert the cable into the backing plate. I seem to recall having to insert it from the wrong direction and twist it around into place.
On the other end, before you hook the cable to the parking brake mechanism in the drum, pull the slack from the cable and slip it thru the slot in the bracket with the pinch bolt. Pretty much like you would do with a motorcycle clutch or brake cable. On my truck I had to take a big screwdriver and open the bracket a little for the new cable housing to slip into it. Initially I didn't tighten the pinch bolt up enough and the cable slipped. Since re-tightening all is well.
Hope this helps and that you have the right part. Don't give up until you try other angles to get it into the drum.
Chuck
