The rear spring change wasn't a recall in the UK. My March 2012 car had weak springs.
It's not a complicated job but it will test your resolve, as a certain amount of strength and cunning is needed to refit the new springs.
http://www.talkmorgan.com/ubbthreads.php/topics/206231/1

The seat runners will work better if they are mounted flat to the floor. If you don't have wooden spacers, it's likely that the single nut which protrudes below each runner will be pressed into the floor and this arches the runner.
Visible here:


DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4