Alright, if you don't mind, here's exactly what I did.
I patched the exe, now my forza shows up as Non-XBL Forza Motorsport on the game list, and the new save folder is working. I made a brand new saved game to check it out.
I unzipped the save file, and I put the UserProfile.xml file into the temp folder is the save resigner, and I opened up the save resigner, chose forza motorsport and then I chose the UserProfile.xml file and hit apply. Then I copied the userprofile back to the save file folder, and I FTPed the folder directly onto my xbox without using the save manager (because when I made a zip out of the folder, xbox manager still didn't find it for some reason) and when I went into the game, it was on the profile list, but it said damaged.
Did I miss something? P.S. The resign info I used was [4D53006E]
ID=[4D53006E]
Title=Forza Motorsport
SigKey=DD46A68DB08C6B0086FDE4F198E0C656
AuthKey=31A43F9B548DB278EF1D0AF8E74BD5B016324526
DataFile=UserProfile.xml
SigOffset=-20
DataOffset=0
DataLen=-20
SigType=NoRoam
Ok, you did pretty much everything correctly, however, I want you to start another new profile or delete that one and start over, then when you open the userprofile.xml file in XSavSig, DO NOT hit the apply button, instead, see if the calculated and current signatures are the same, if they are not the same on a fresh new save, your HD Key is WRONG. You must first fix that problem before you can do any hacking of the save or resigning.
If however the calculated and current signatures are the same, you are doing something else wrong, but I am betting that it's just a wrong HD Key, that is the problem 99.999% of the time.