Got it apart! clutches fused to steels.

We locked the output shaft in a brass vise on a bench, and double vise-gripped aluminum around the input shaft with a choker cable over the visegrips and a 1 ton come-along. End up pulling the snap ring over
the end of the output shaft and the hole mess feel apart. Rear clutch housing isn't blued, but it has some brown (on the outside!) also broke
the splined housing on the front of the rear clutch (wacking with a rubber mallet).

The Belleville spring looks fine.

The planetary gears look a little rough on the edges and some deep scratchs on the alum planetary carriers.

Any idea what caused the failure?

Thanks for your help!