I made two of the shortened extenders for the front of this buggy. The way I drilled out the 8mm hole in the insert is by lining the 1/2" aluminum rod up vertically and then drilling through one of these extended hexes to keep everything aligned. Otherwise, I would never have been able to center the hole properly:
I drilled the pin hole simply by clamping the hex to the drill press table with by its flats - keeping the pin hole exactly at a right angle to where the axle will go through:
I JB-welded the insert into the extender and then filed it down to exactly the right length so I could get one shim between the extender and the bearing:
With these on the front of my buggy, the width is now around 18" (about an inch less than before). The rear width is 19.5"
I like the way it looks, but I'll have to see how it handles.