The English at that place: not so good. I corresponded for about a month on an A-arm suspension, just trying to get a wheel travel spec. I finally gave up.
I think that adapter and those bolts are going to work. My concern with ordering the bolts from the UK is that the adapter ring will likely not have the proper angle chamfer, since metric chamfers are also different than SAE. Getting your adapters remachined will likely cost more than the whole Italian set-up.