From the information I found, Fang Performance Inc. was a company located in Kendallville, In.. They offered body kits, and other pieces to modify Mustangs. In my opinion... the company was trying to become like Saleen or Shelby. You were able to send your car to them (or purchase items from them) and they would do the mods to your vehicle. One of the packages they had was a tribute to the 1969-1970 Twister Special Mustangs. Fang Performances' version allowed choices such as...their version of the Shaker hood scoop, pedestal rear spoiler, non-functional Hood twister down locks, Original style Mach I stripes and Twister Special decals, painted Widow peak style fiberglass hood painted with the 69-70 style stripe, and black Honeycomb panel between the rear lights.
They also modded cars with other packages that included the Mystery named items that included longer hoods and headlight eyebrow extensions to give the 2005-2009 Mustang front ends the "hooded" appearance of the 60's stangs. Unfortunately... they didn't stay open for long, and there is not a lot of info about them on the web. Hence, the reason for my pleas for info about them, and their modded vehicles.
I can't remember where I saw the term FangStang
... But decided to use it as a forum name. To me it is short for Fang Mustang.
Sold it in 2013 to get a truck... and the Fang!