I started Sunday morning by looking for the part that I thought I had bought.  It was nowhere to be seen so after a lot of head scratching I decided that perhaps I didn't buy that section after all.  So I continued with the rust removal.

I decided to make a 'jig' for the section of the L shaped metal that needed replacing and essentially screwed it to the bench then cut out the rusty piece.  I cut the new replacement section to length and welded it it as shown below:

 Having replaced the section I painted it.  All done for the next time.