An additional "sleeve" of a smaller diameter tube was cut so as to extend into the original structure.
The new tube was slid back into place and a 1/8 in gap was left for welding. Also notice the holes for the future rosette welds.
Once the spider plate was squared and vertical, the longerons were marked.....
...and the tubes cut to match.
All four longerons were trimmed. It's beginning to look like a Nieuport again.