Righto, helpful post time.
180 = 180.
If you try and bodge it without the conical washers you'll have a bugger of a job getting the thing to work, the Ashima 180 adaptor comes with a pair of shallower conical washers/bolts though, with a shorter thread to accommodate the smaller disk, so that is good. The bolts actually look a wee bit short to my eye, but it's a post mount, so shear loads should be fairly small and well, if the rotor bolts'll hold then sod it, eh?
Is this place still populated by weightweenies? It is? Front = 109g @ 180, rear 80g @ 160, both a nadge under the claimed weight. Old Avid G2 dinner plates off HMS Norco = 190g each. Mostly, though, I'm most pleased about having a rear brake that'll no longer lock up when the lever gets a light headwind on it.
To satisfy the other camp, no I did not weigh my last evacuation so cannot say how much one could save by merely visiting the house of easement, but (a) I tend not to ride with a turd wrapped round each hub so the comparison is essentially flawed and (b) I've always wondered when that analogy bobs back round the u-bend; why not have a crap and a lighter bike? Radical, I know, but that's how I roll.