I did a manual swap on my 89. Your 91 is like my 89, not sure if the pedals will swap. I know 1986-dwn will not swap.
I used a 89 donor. The driveshaft was different. I could have used my auto driveshaft, but the 5 speed shaft was thicker and had larger u-joints. I had to swap the yoke on the rearend so the u-joint would fit.
I had to get the upper shirt crossmember pieces for the rear crossmember. The zf set back 1 inch longer than the c6 auto I had and the upper crossmember pieces are offset more.
I got the harness for the transfer case and 5 speed transmission. It plugs into the plug under the brake booster. I unplugged the automatic harness, and plugged in the 5 speed harness, not wiring required, everything worked. If you do not have this, the first thing that will happen after the swap, the truck will not crank. That is because there was a neutral safety switch in the auto harness. You have to jump these wires if you do not have the proper 5 speed harness, which has a jumper made into it.
I had to take a piece of wire, and tie up the lever down near the steering box for the auto shifter. If you don't, the lever will fall down and the old auto column will think you are in gear, and not let you turn the keyswitch all the way to off. Tying it up will let it think it's in park all the time.
Make sure you get the transmission cover for the 5 speed. It's higher for clearance. It's best to take the seat completely out to give you working room and room to pull the floor mat all the way back out of the way. Gives you lots of room to lay there and swap the pedals also. Swapping the pedals was aggravating, they ran the speedo cable right through the middle of the pedals. So you have to pull the cluster, disconnect the speedo cable to get the pedals out. The 93 might have a electronic speedo and you might not have this problem on it.