Torque converter/flexplate on cast crank 340
The 727 flexplate has 3 different bolt patterns to cover just about everything and has a larger overall diameter. The 904 flexplate has 2 bolt patterns and has a smaller diameter. The only difference is the extra pattern on the 727 within the extra diameter. They include 5/16" and 7/16" holes.
I have used the 727 flexplates with a 904 without a problem. But some people have had a clearance problem with some older Mopar mini starters. I'm not sure about the larger OEM starters.
Do you have the 904 converter yet? If so, measure first.