Are all 360's balanced the same?

360 with a 904 = B&M 10239 Flex plate. Done.

Best way to do it.

Make sure you use the correct "thin" flex plate bolts (with red loc-tite) when you bolt it up, or they will rub the trans when the converter spins.

Vibration Damper. I like the Mopar Performance 360 Damper. P5007301