The pipe is 3-1/4" OD, 2-3/4" ID, 7-1/2" long with a 3/8" thick plate welded to the top. Inside the pipe is a bronze bushing 2-3/4" OD x 2-1/4" ID running the full length of the pipe. The mounting plate is 3/8" T, 4-1/2" W, 6" L. There are 3 holes per side for 3/8" bolts. The outer slot for the key is 1/2" wide x 2-3/4" long and 1/16" deep. The inner slot is 1/4" wide x 1-3/4 long. There are two holes on 2-1/4" centers for 10-24 bolts.
The screw is 1" dia. Acme thread 11" long. The top 2-3/4" was turned to 3/4" dia. There is a needle roller thrust washer sandwiched between two thin steel thrust washers that bear against the inside of the 3/8" plate on the top of the pipe when assembled. The other washer on the left end is a bronze thrust washer that goes between the handle and the outside of the top plate. (The screw is not bent, by the way. Fisheye from the camera lens.)
This is the pipe that holds the large wheel and rides inside the pipe in Photo1. It is a couple of thousands under 2-1/4" so it will slide smoothly in the bronze bushing of the larger pipe. The pipe is 7-3/4" long plus the length of the Acme nut welded to the end. There is a 1/4" key slot running the entire length. The yoke on the bottom is made from 3/8" plate and is 2-3/8" wide inside. The axle center is 4-13/16" from the inside of the plate. The axle is 17mm dia to fit a 6203 bearing in the large upper wheel. The threaded end I made 5/8" NC.
The handle has a major diameter of 2-3/4". You don't need to have the smaller diameter but I thought it looked better. The spokes are 1/2" dia. x 5-1/2" long. I drilled six 1/2" deep holes at a 10 degree angle, then tacked the spokes in the holes. Start out with a 6" length and round off the end that will be sticking out. The handle is secured to the screw with two 1/4" set screws. The center hole is bored and reamed 3/4" for a nice fit on the screw.
Photos 4 & 5 show the support for the lower wheel and the key. The key has two holes drilled and counterbored for the 10-24 screws, 2-1/4" C-C. The 1/4" wide key for the slot is 1-3/4 long x 5/8" deep. The total height of the piece is 1". To clarify, start with a piece of stock 1/2" wide x 1" thick and 2-3/4" long. Since I included several views, you should be able to decipher it. File the ends round and your good.
The lower wheel support is 1/2" thick x 1-1/4 wide x 1-13/16" long. I started with one long piece and then cut it in half through the 1/2" hole as seen in Photo 4. Machine a 1/8" "rabbet" along the sides, both in width and in depth. That will leave you with a 1/4" wide key that slides inside the lower yoke. Remember to give yourself a little clearance or just plan on filing them to fit.
The lower roller is 3" wide and has a R8 bearing in each end. These have a 1/2" ID. The major diameter on the roller is 2-7/8" x 2-3/16" on the ends. The axle sticks out about 9/16" on each side.
End view of the roller shows a 1/4" hole on one end only. This is to drive the roller for machining the OD while mounted on a mandrel.
There it is. Between this post and the previous one, I'm sure Surly can take it from here. Maybe there will be a set of finished drawings available at a later date for anyone who wants them. I hope so - can't wait for the royalties to start rolling in! In the meantime, if you decide to make one for yourself no guarantee expressed or implied, user accepts all liability, blah, blah, blah.