To start I cut the round tubing to the proper length, I fit the square tube to the round tube and I cut a couple of pieces of plate to a little bit larger than the required size.
Next, after drawing the dimensions on the plate, I drilled the holes that are for the rod end bolts and put screws into them to keep them in alignment.
Next I cut the plate to approximate size with a hack saw and then shaped it to the final size using a grinder.
The next step was to weld the spuare tubing to the round tubing.
Then I clamped the flat pieces to the square tubing at the proper location and welded it. If you look at the larger picture you can see I used a cut off piece of the square tubing to hold the plates apart as I tightened the screws down.

Here is the finished walking beam.





 

Here is a close-up of some of my welding.