Magnum Swap column vs. console shift

64? should be a 904. Is it a cable setup with the center console? just like the push button shift. Mopar Push-button transmission tech tips
If so all you'll need to do is fab up a different cable. Or modify the cable end. the 904 with cable shift is internal in the trans unlike the 46RE
I would be surprised if you had a 727 in a 64 unless it was already a swap. In order to fit the 727 you would have to fold the pinch weld where the trans tunnel meets the fire wall. In order to fit the 46re you need to do alot of massaging of the tunnel and some chop / cut -n-weld for the overdrive unit... lol fun fun...
I have a 65 and I'm doing the same 46RE. I'm using the center console shiftier that's a cable shift.
If you scroll down page 4 you'll see what i'm working with...
1965 Barracuda MMP

Hope this helps... If you need any more info on this hit me up.
Good luck with the build...