An added thought on your truck.. Reviewing the pic you attached I noted that your truck appears to have a floor mounted emergency brake that is attached to the back of the transmission, the drive-line then attaches to the back of brake hub in lieu of having a slip yoke. If my assumption is correct you have a problem with changes to your trans because in doing so you will eliminate the hand brake.
If you go forward with a trans change, you will have to find a hand brake assembly out of a '64-66 C-10,20. Wm.
