"Easy" depends on the person and tools availible. I found it reasonably straight forward, but time consuming. I got a little depressed and went and built a rear bumper while doing the second side to regain my sanity after perpetual rust. I did completely removing the sills, replaced a fair ammount of the floors and bulkhead foot wells at the same time.
I used two 1.4m lengths of 100x50x3 box section and made new body mounts on the insides using 3mm plate. This size of box was about the same height, but a a bit narrower than the origional sill. 120x60 may be a better size, particuarly if you want to weld some tree sliders onto the sides of them. Just replacing the origional sills with box section without some form of tree sliders on them won't protect the bottom of the doors :roll:
