Chuck, The cab corners wrap around the back of the door piller just like original back skin would have. I also had a pair from another mfg. that I had bought before these came available. Hands down better fit from these. I also used their inner cab corners. I wish I had a chance to use their cab mount cross supports as mine were junk and took a lot of fitting. These were not available when I put mine in. I have heard that these panels were made off templates from a rust free cab by the owner of bowtie bits but I am not sure of the relationship to Keyparts unless they are the ones producing off his templates. It is nice to try to see someone attempt to make a relatively correct patch panel.
The only other panel I wish they made is a Toe board as what is out there will work w/ lots of fitting, but could be much better.