Well… for starters…from the STOA site
…"TAC criteria:
TAC inspects for:
* Authenticity: a Tiger unibody as produced on the Jensen assembly line.
TAC does not inspect for:
* Originality: a complete Tiger identical to the car as originally produced by Rootes.
* Correct ID elements (VIN, JAL, etc.)
In other words: fender flares, hood scoops, highly modified engines, custom interiors, etc. do not have any bearing on the TAC procedure. Many highly modified Tigers have been awarded TAC certificates."…
Taken from C.A.T