I don't know if this is always true, but it appears that the way you can tell is if there is a "T" on the lower right of the 6580 badge on the front.
I didn't see this in the documentation anywhere. The controller inside is significantly different (3 boards instead of one). +--------+ | IBM | | | | 6360 | | T| +--------+ There are a couple up on eBay right now from seller 'potomacestore' Double-sided 6360s seem to be much less common than single-sided.
