Just did this swap this last summer in my old 66 GMC Suburban. I learned a lot. I used
http://www.bowtieoverdrives.com/ cable and linkage kit . They have a great write up on how to set the cable and tune the linkage to the trans. ( probably saying that wrong ) Shortened the driveshaft and moved cross member back , used stock shift linkage with a few mods. Also put in a lock up converter switch in the side of this trans. Seems to work well .