Does anyone make the engine compartment liners that close off the frame rails?

I'm not aware of any vendor that offers an inner fender panel replacement (whether complete, or just the bottom strip).  If the rot on your car hasn't travelled too far up from the frame rail seam, the panel is pretty straight from front to rear and it shouldn't be too difficult to graft in new metal cut from flat sheet (20 gauge, IIRC). 

A CZCC member from Calgary, Alberta (name?) posted a detailed build about 2 years ago that illustrated this repair quite nicely.   

KF Vintage JDM has them for the 240Z, they go up to just below the shock towers. I'm not sure how close they are to the 280Z but might be a starting point. I purchased a pair to use on my resto. They can be purchased individually.

 

Wonder how different 240 and 280 sheet metal is. There are alot of 240 parts.