I have the answer to my own question, but maybe someone wants to know what that answer is, so...
To determine if your timing chain needs to be replaced without removing the covers is done by removing the distributor cap, than rotate the crankshaft, the rotor should react directly on this movement, if it doesn't it means there is space on your chain. There's allways a little space, this doesn't matter.
I still don't know if there's a difference in a fender from '72 and '73, but I think there is because on the site
www.vamustang.com the two fenders have diffent codes. The '71 & '72 fenders have the same code and the '73 fender has another code. Does anyone know if this means they are different?