You know its weird, because I remember everyone saying that too. But I didnt have a single problem - just bolted right in. Odd.
AFAIK, there is no difference in fuel pump. Get one for a '66 mustang. Double check on the forum @ fordsix.com
Ask to see both the 1964 Falcon 200 and 170 and see if there is even any difference. My bet is there isn't.
I have used fuel pumps from all 200's..they all will bolt up and work with the only mods will be the fuel lines. the best stock pump is the 71-82 Mustang/Maverick/Fairmont/Comet...... these are better than the early falcon pumps since they don't tend to leak out the weep hole on the pump..but they don't look as cool. Just a good solid pump. Fordsix.com is ok but I like the Hamb better. Best of Luck FrankBoss www.PintoWorks.com