Hint
#1 -
Now and ThenThe letter that was submitted to the document examiner was a copy, so paper examination(s), such as watermark dating, could not be undertaken, nor were they necessary (for this particular case)
The type font is Courier 10 which was in use in 1961, so no help from that corner.
It will help if you are over 50 years old (60 would be even better), so if you're not, get some help from someone who is.
Use your common sense.