The JAS-39C to E conversion sounds a little more comprehensive than a simple 'upgrade' though, '(new) primary structure' sounds like quite a significant part of the airframe will be a new design and build...
-RP
I think the words are misleading, it isn't a
conversion or an
upgrade of the existing 39C. They are brand new aeroplanes with new engines, larger airframe (to accommodate the larger engines), AESA radar and other differences.