Apache Header Tampering

Can someone point me to the right track? On this one, I found the hidden directory, used an X-Forwarded-For: to see into that directory where scanning for files showed a lot of 404s, with just a few 403 response codes. I've tried everything I can think of with variations on X-Original-URL:, X-Rewrite-URL:, and X-Forwarded-Uri:, but none of them get me able to see into any of the files/directories. I've even tried a few variations instead of X-Forwarded-For:, such as X-Client-IP: and a few others. I feel like I must be missing something. I didn't find any actual .php files in the hidden directory but the question seems to indicate that there are some in there.  I found what I think are other directories within that first hidden directory.