Maybe so, but would typing that letter on the IBM Executive have the *exact* overlay that typing it on MS Word does? I think not.
I work at a Help Desk. One of the partners in my firm wrote a book when we were using Word Perfect. He wanted to print out a few more copies but we had since converted to MS Word. Now, we used the same computers (different software, though), the same font (Times New Roman, coincidentally), the same pitch and could not get the text to line up exactly. We had to change the parameters (i.e, condensing white space, kerning, line height spacing) for almost *every line* in a 200+ page book to get the same line breaks and page breaks in Word as we did in WordPerfect.
And this was no 30 YEAR DIFFERENCE in technology -- no more than 3!
So if you can show me that you can get an exact overlay from a 30 year old typewriter as you can from MS Word I would be very interested to see it!
The spacing between letters, both horizontally and vertically, is a function of the font, or typeface. So it is possible that the docs could line up.
Knowing IBM, their implementation of Times was probably perfect. Knowing MS, well...maybe not. Then again, perhaps the doc was produced on a Mac, which would probably be right.
My point is simply this: we seek proof, not speculation, and it seems to me that there are better indicators than the typography that this doc was forged.