The biggest change is the instrument cluster in 65. You either have to do a conversion, or put in a new wiring harness altogether. I personally am taking my 65 back to standard interior, as the P.O. had done a partial Pony upgrade. I tend to want to put my car back the way it was, though. Just my .02.
1965 convertible "White Pony", my own lesson in mechanical humility
You'll have to get new seat buns (foam) too, as they are different for the pony interior. The simulated woodgrain wheel is expensive, about $400-600 restored. What's more, you'll have to cut holes in your doors for the courtesy lights. If you want to go with original or NOS Ford items, conversion to pony interior can be very expensive.