Pre-magnum flexplate on a 46RH?

Alright fellas! Happy to help. Our 408 is balanced on the rear as an LA 360. So we recommend an LA 360 balanced flexplate.

You are correct that the factory flexplates were neutral, but the commonplace aftermarket is a NEUTRAL converter, and then you use the proper balance flexplate.

Some transmission companies do still balance the converters but most don't

I guess My answer would be I don't care if the flexplate, or the converter, get balanced to LA 360, but one does, and one needs to be neutral.

Next thing would be to make sure that torque converter is stalled properly....a factory one will kill that engine.

If its a Magnum balanced converter that you happen to have already.... knock the weight off and get an LA 360 balanced flexplate

The later model chrysler transmissions kept the same 727 or 904 converter patterns. I just don't remember if the 518 was 727 or 904 based without Google.

Let me know if questions remain after all that!!