there not that simple, its not a simple bit of square box section, there is quite a bit of fabrication involved.

To get it to work right and last involves quite a bit of work.

Depends where you start from really, i.e fabricate from new, or chop onto an old arm.

I much prefer the 1st idea, and fabricate a completely new arm.

There are also about 4-5 different way to do it.