The T-5 in my truck came from an 85 S-10.
You've already noticed that there are lots of threads on the t-5 conversion for a AD truck. It should be even easier with your truck, since you don't have to worry about changing the rear axel.
46 in progress makes a very good point- IF ther is nothing wrong with your existing 3-sp (and I think there is) what you need to do is fix your 'final gear ratio' Which is the transmission gear ratio times the rear differential ratio. In your case it should be easy. Either you'll just have to swap the pumpkin in your rear diff for one with better gearing, or you'll have to buy/find a ring/pinion set with better gearing, depending on which rear end you have. That would probably be cheaper and faster than doing any tranny swap.
If your tranny is beyond the point of repair (or past the point where you are willing to work on it), putting in a t-5 would be a cinch.
Call a few junk yards in your area that'll let you pull your own parts and then go there and scout them. Look for 4x2 Blazers, S-10s and Astro-vans. Find the one with the lowest milage and a 5-speed, and pull it. They are easy to get out. Just a cross memeber, drive shaft, four bolts and the back up light plug. If you've got several to choose from, my advice is to look for telltale marks of a rebuild- like for example new permatex between the tailshaft and main box, or the cover and the box. Be sure and grab everything you can get your hands on, especially the the back up light pigtail, clutch disc, shifter, and the yoke off the S-10 drive shaft. You'll need the yoke to get your driveshaft to work with the t-5.
After that it should be a cinch to install it. It should bolt right up to your bellhousing. All you'd have to do after that is change the fluid, find a clutch disc the same diameter as your pressure plate/flywheel, shorten your drive shaft, and cut a hole in the floor board for the shifter.
I'm guessing you'd pay $100 for the tranny, $50 for the clutch disc, $10 for fluid and $50 for the drive shaft work.
I think in '63 you could get a truck with an automatic, so that is still another option for you, and shouldn't be hard to mount to your engine- Same thing as a t-5, find the tranny you want and grab the flex plate, torque converter, bellhousing, backup light pigtail and yoke. then all you'll need to do is buy yourself a shifter!
PS-
I like your new title!
