I always like to be planning several steps ahead. I really want to drop the floor at least 50 mm. More like 75mm to 100mm. I saw this 39 Packard chassis on display at Gilmore in Michigan last year. Little did I know that it would come in handy .
Working on both Jensens and the 260z recently, made me think like a unibody. On both, the sill becomes the structure. The original side rails are rusty and thin and come diagonally through the footwell. . By widening the side rails out to the sill line I can drop the floor between the rails. The X member can then be sectioned and beefed up.
It might look like a lot of work but I have to do it anyhow.