So I tried the stainless bolts and acorns...but sheet metal screws actually seems to have more purchase and be more secure. I cut little metal strips to sit under the scuttle that I drilled though and put the screws through, to provide more support I covered the pointy tips with small #6 acorn nuts held in place with RTV (a ridiculous bodge if I ever saw one!)
Came out pretty good - I'm happy with the results, also quite surprised by how effective the little screens are for wind mitigation. To counteract the slight curve of the dash laterally, I flipped the outboard lollipops on the screens so that the mounting posts were lower than the inboard lollipops. This effectively raises the outboard side of the screen just enough that the screens appear straight in relation to the windscreen.