+1. Keep it. I still regret selling my 70 Mach 1 back in the day. It would have been fun being able to switch back and forth depending on my mood. Yes they are different beasts and the S197's are much more civilized and fun to drive, but as they have said before the 65 get alot of stares and attention. It probably isn't costing too much to insure and it will appreciate in value as time goes on.

DON'T sell it if at all possible and tuck it in the garage! you won't regret it

 

Keep the '65 and get a new one as well. Nothing is better the 2 ponies in your stable. I have had my Caspian Blue '65 convertible for 10 years and absolutley love it. It is my sunny day driver in the summer and I just picked up a '07 GT/CS as my daily driver - way to much fun. So if you can afford it keep the classic as it only goes up in value each year and get the new stang. You may also need a great wife like mine who works extra shifts as an ER nurse to help pay for my Pony Passion!!!

Good Luck!!!!!!!!!!!!