Small Pilot 904? Need help identifying correct transmission

I'm restoring a 64 Barracuda and bought a 66 273 that has a pilot bearing diameter around 1.5", which is smaller than the 727 I was hoping to put in. I have been told that I will need a 18 spline 904 to get the torque converter with the right pilot bearing diameter. My open question is: Is that info correct or are there other options? Anyone had this issue? What do I need? THANKS!