65 and 64 valiant parts interchange

Why do you have to swap the valve body? See here.

Why were the pushbuttons dropped? It was not because of the National Highway Traffic Safety Administration (which didn't exist until 1970, and its precursor agencies didn't exist til '67). Chrysler dropped the pushbuttons after the 1964 model year—that is two years before the National Traffic and Motor Vehicle Safety Act, and four years before the advent of the first Federal Motor Vehicle Safety Standards. Chrysler’s takeup of shift levers had nothing to do with any Federal safety standards; none existed at the time. It was primarily because they felt with conventional controls they’d sell more Chrysler vehicles to driver’s-ed programs, and this was considered crucial because it was some of a new driver’s first real vehicle exposure, which was thought to be foundational for vehicle preferences.

Moreover, the pushbuttons were regarded as something of a played-out fad; they’d been introduced in 1956. They were dependable and didn’t make trouble (unlike the Rube Goldberg electrical crapmesses on the Edsel and Packard), and were regarded, even by Ralph Nader, as safer than a lever. But the tailfins-and-pushbuttons-for-everything age was in the rearview mirror.

The actual safety standards influence on automatic transmission controls was to force GM to change. Many GM quadrants were arranged P—N-D-L-R. This was (correctly) regarded as dangerous because a forward and reverse position were immediately adjacent with no effective lockout. In the absence of Federal vehicle safety standards, the Goods and Services Administration drew up their own list of standard equipment required on cars purchased by the government. The list included front and rear seatbelts, nonglare windshield wiper arms, windshield washers, a driver’s sideview mirror, reversing lamps, and automatic transmission controls with no forward and reverse position immediately adjacent. The GSA requirements had the effect of making those items standard equipment even for cars not bought by the government (automakers weren't about to make government and non-government versions of their cars), which is why things like backup lights and sideview mirrors and screenwashers moved off many models’ option list for ’66 and became basic equipment. GM, having previously issued smug dictates that they were the market leader, so the rest of the industry was just going to have to go along with the GM way, were forced to adopt the safer P—R-N-D-L. When Federal Motor Vehicle Safety Standard № 102 then came in, it stipulated that a neutral position shall be located between forward drive and reverse drive positions, re-sealing the fate of GM’s unsafe design.

History repeats itself: now we have new Lincolns and some other vehicles with electric pushbuttons arranged P-R-N-D-L.