panel behind doglegs

Hi Folks, i'm finally back on my 73 Z resto after a year off replacing the roof on my house and a complete paint job last summer. (developed a leak and one thing led to another). I've decided to do all the cutting and welding myself so I bought a Lincoln mig welder and have done alot of practicing and I'm ready to get after it. My question is about the panel behind the doglegs that sandwiches behind the rocker panel end and the dogleg.

Right side was completely gone and left side is mostly there but i need to trim off some of it. Does anyone sell the panel or do I have to make one myself? I have the doglegs and rockers from tabco, just wondering about this other panel, i know I have to put something back in there. Thanks.