superbird rear veiw mirror arm??

[DoubleDlover]

Ive been looking to replace my rusted arm that my rear view mirror hangs from on my bird. But everytime I grab one from some car its always a different length. Sometimes long. Sometimes short. Now im wondering if the arm on my car is even the right one.... Does anyone know the correct length for a bird? Probably same as any 70 roadrunner or coronet?? And a total length would probably be the best. thanks r