The inner sills and floor pans for a sidescreen TR are made correctly by Heritage in UK. The outer sills are not stamped but bent on a 90 degree brake press that is usually used for bending sheetmetal. As a result the outer sills are flat from one end to the other. Also the 90 deg. bend is more like 88 deg. so the flat surfaces are curved in (concave" a little bit. These need to be reworked. I have used a large rubber mallet to hammer them into the right curve to match the curve along the bottom of the door for my own TR3A. On another TR3A, I asked a sheetmetal shop which had a rooling wheel to get them right for me.
I bet you thought that the door and the outer sills were straight from front to back. Check them out. They have a slight outward curve. If you leave the new repro sills "flat" you will end up having to trowel on about 3/16" thick Bondo on the outer sills to match the curve along the bottom of the door.
Also, at the front end where the outer sill is welded to the bottom of the "A" post, there is a pressed "clearance" for the bottom front corner of the door, so that when you open the door fully, the "clearance" is to prevent your door from getting bent (pinched) outwards for about an inch along the bottom and up the front door gap.
This "clearance" is too small and you will have to re-work it to provide enough clearance. Clamp the outer sills into place, mount the door on its hinges, tighten the hinge screws and slowly open the door to check this out till you have enough clearance. Then you can weld it on.
Finally, the repro outer sills are too short and you will have to MIG weld in about 5/8" of new sheetmetal at the rear near to "B" post.
If you can find and buy correct NOS outer sills, then you should be able to save all this extra work. But the retro ones I bought 20 years ago were as described above and in my photo from 1989