I am in the process of swapping my T221 out for a NP205, behind a SM465 in my GMC. If I had a good solid day of nice weather and no work/school, I could get it done, but no such luck.
What you will need for the swap:
-NP205
-adaptor
-bolts for adaptor
-coupler sleeve
To make things a little easier, I took the seat out of my cab and unbolted the high floor hump. Removed driveshafts, front is a ***** to get off.
Now its time to unbolt the Rockwell...I decided to take the transfer off first, and then the adaptor (separately). there are 6 bolts that are around the perimeter of the adaptor, take those off.
then you will notice a little access cover on the drivers side of the adaptor w/ 2 bolts holding it on, take those off. You will uncover a small cavity, there are 2 more bolt heads inside here that you must remove to get the transfer off. This took me a real long time to figure out, why the transfer wouldn't come off. make sure you don't get your wrench stuck in the cavity.
after that, it should come off fairly easy. make sure you take the speedo cable off before you drop the case...lol.
i found out that all the bearings and seals in my transfer had gone bad, but i think its rebuildable...oh well. i also discovered that the coupler sleeve and the transmission output were both pretty worn
so I will have to replace the transmission sometime in the future, too.
now comes the FUN part...you will have to unbolt the crossmember and the torque bracket from the frame, and move the whole thing back approximately 1-1/2 inches. this isn't an exact measurement, I would recommend bolting the NP205 adaptor to the transmission and crossmember, and then marking where the bolt holes are.
then drill the 8 holes out, having a right angle drill will make life easier for the bolts on the upper part of the frame. then bolt the crossmember up to the frame.
this is as far as I have gotten, the NP205 is ready to go in, just waiting for some nice weather (working out in the driveway and i'm picky, lol). from observing what has happened, I expect to have to get my rear driveshaft shortened and my front lengthened. ideally, i'd like to find a 1 piece driveshaft from an original SM465/NP205 truck, as my truck came stock with a 2 pc, but I will have to keep looking. also, the shifter will come up on the passenger side of the hump, not the drivers side, so you will have to cut a new hole.
i think that is all, if you have any more ?'s feel free to ask.
EDIT: just remembered...good luck finding an NP205 or Rockwell. They seem to go for quite a bit of cash. Same with the SM465/NP205 adaptor.
I was lucky and got (2) NP205's, (1)4x4 SM465, (1) adaptor, and (1) like new coupler sleeve for a grand total of $30....so the good deals are out there. However, I was quoted up to $175 from this board just for the adaptor, so I would advise you to shop locally if possible.
Another note, some 1970 trucks had an NP205 with the shifter on the drivers side, you could find one of those and forget about cutting your floor hump and relocating shifter.
Yet another note, SM465/NP205 adaptors from '73 and up trucks are stronger than the older versions, in case you wanted to be lazy and forgo reattaching the torque bracket.