I have a 73 E Body 340 with Air Conditioning 26 inch Radiator in my 74 valiant 4 door with a factory 26 inch radiator opening just had to redrill 2 holes to use existing mounting holes.
Used a pair of paint sticks between the radiator and the lower core support to space it correctly.
Also used a radiator fan shroud from a 1980 CMX Mirada 318 auto Air Car with 26 inch Radiator