[R-390] Collins s/n marking

[w4thq at cox.net]

A Collins AF unit has the following stamping:

FINAL AUDIO UNIT
     540  7553  005
COL  SER.  NO.  323

A Collins IF unit has the following stamping:

FINAL I. F. UMIT
   540 7577  006
COL SER. NO.  221

I am curious about the word "Final"

John W4THQ