Need some advice

It all depends on what year 273/904 you're getting.
Your car uses a ball & trunion driveshaft. 904s up through '65 also used a ball & trunion output shaft. '66 and later used a slip yoke. Use of a later 904 in your car would require a new driveshaft in addition to some of the mods listed above. You will also need the early A body V8 cable operated pedal and throttle linkage, and the transmission kickdown linkage. Your '64 with a slant has a rod style throttle linkage that is incompatible with a V8.
If it's a later 904, you can put a floor shifter in it, or swap in a '66 automatic column if you want to have column shift. The columns come in 2 different lengths- one for manual steering and a shorter one for power steering.
If it's the earlier 904 you'll have to locate the proper pushbutton assembly and cables, and the proper dash trim.
Aftermarket cable operated floor shifters are not compatible with the early transmissions- they're generally designed for the later model ones.