You might be able to squeeze the spring out with the seat in place but it's so easy to get the seat out that I wouldn't struggle with it in.
The front mounting cover is held by self tappers into the wood, and the seat belt mounting. I can't comment on the order in which you do this job on Morgans, but access to the U bolts is almost impossible unless you block the spring in a compressed state, and then it becomes dangerous to un-compress. So that may be correct. What does Go-Mog say, because it's a fundamental of Morgan DIY jobs so I imagine there are some instructions on there.
