1972 dart 360 with 904

If you're dead set against using a B&M flexplate (I would), another option is adding weights to the convertor, like the factory did. DC/MP used to offer kits for this, but they have not been available for many moons. So, you're left with making your own. There are weight specs and mounting diagrams on the internet, but you'll have to do your own legwork on that.
Lastly, there's a balance plate from Quick Time, that mounts between the crank flange and flexplate.
Quick Time | RM-531 | Automatic Transmission Flexplate Balance Plate (fpautoparts.com)