Yes the orginal steel pressings have a curved profile on the top lip of the sill, I cut slots in this to allow it to curve and match the profile of the original.
If you are just replacing the outer skin, reinforcer and lower inner section it isnt really necessary to brace the shell. Axle stands under the subframe and rear axle and just dont move the car! I braced the door gap on Richards just where I cut off the top of the sill section to gain access to the reinforcer. I was worried about the inner section folding in on itself where I had cut the lower section away. I would brace the doors as well as at the base of the B post to B post across each other and bottom of b post to top of opposite B post creating an X if I have to cut a lot of the floor or inner sill out, but I haven't had one that bad yet! Although, I know Alun has one lined up for me!
Sorry Steve and Dave, I didnt reply!
I dont cut off the lip, I bend it down slightly to create a sort of drip rail plus I use it to line up the sill! My concern with cutting off the lip is that water will travel up into the seam through capillary action, which is probably the cause of rust here anyway! Plus its stronger with that lip. I do put three drain holes in, but drill a hole in the corner of the inner sill then bang the lip over t make it look like the original, you just cant see them well with the lip on! The seam does get a thin bead of seam sealer and as we all know, the sills should still be protected internally with a good cavity wax.