Use the perch bolt or a 5/8 bolt to assemble the bosses on the axle. Put a thin piece of card (cereal box is a good thickness) between the axle and one boss.

Nest the c-plate against the bosses and slide the plate along the boss. It will probably slide about ¼” total. Split this amount and tack the c-plate to the bosses.

Remove the assembly from the axle and finish welding the bosses to the c-plate. Repeat with the other c-plate.

The main plate is 3/8” thick and the c-plate is ¾” wide along the long flat section. An easy way to center the main plate on the c-plate is by holding a piece of 3/16” material against the side of the main plate and then make it flush with the edge of the c-plate. Tack the main plate and then finish welding.