That’s some great work that takes time and patience! Fantastic job, Congratulations

I looked a bit before I bought these replacement frame rail section from KlassicFab, but did not find helpful information regarding how well (or not well) they fit. Well... they don't fit my 1971 240z very well at all. The front most and backmost part of them touch the floor with a large gap in between.

The tabs on the front don't match up very well. The left side frame rail had been "hand manipulated" somewhat (3rd pic here):

Even after the manipulation, the height of the front was incorrect - the bottom is too low on the outside surface, but about the right height on the inside surface.

Anyway, I didn't have much of a choice - I needed to make them work. To do so, I cut out the sides at the "turn" that they make at the front of the floor, towards the compression rod box. This allowed me to re-contour the bend in the bottom surface of the frame rail so the rails fit the car's floor. Then I made replacement side portions of the rail that locked them into the position my car required.

Additional work to recontour the back of the frame rails to fit the floors was needed as well (3rd pic above). The left side needed recontouring at the front of the frame well also. And both sides need "extensions" on the inner side of the frame rails too as they are not as long as the originals.

Lots of hours so far to get these to fit - just so you know should you decide to purchase them. They may fit the 280z better. I don't know.

Surprising they are so far off KFvintage has a good reputation. Maybe send some feedback to them?