I started out today by confirming the measurements & angles of the aft seat side rail plates.  These plates will get welded to the top side rail pieces and will sit just aft of the front seat & against the longerons.

To make these 1-1/2″ high plates, I needed to weld two 3/4″ wide 4130 strips together.  I prepped the edges of each 4130 strip.

I could have spent a fair amount of time practicing my TIG welding, but I figured I would start in and give it a try.  Having a fair amount of experience welding I knew the difference would be between good looking strong welds–with a good amount of practice–or strong welds that may not come out as sexy looking.  Another issue was that the filler rod I have on hand is a little too big for this weld, so it was a bit of challenge in adding filler metal to the weld.

Here’s the resulting ugly but effective weld.

And here’s the piece after I cleaned it up.

I then marked it & cut it diagonally so that the separate pieces fit in the aft seat spot.

After tweaking the aft seat side rail plates for each side, I prepped the right side top rail piece (shown in the pic above & below) so I could weld an extension tab onto it at the aft end.

As a reminder, I should note that when I originally widened my fuselage by 1.4″, I also widened all the longerons from the front seat aft, top & bottom, to bring their inside edges inboard to allow the engine mounts to fit correctly.

Here’s the right side rail below with the extension piece added on.

I did the same for the left side top rail, welding an extension to it as well.