How did 7 come to be an abbreviation for 'and' in Old English? is a beautiful question about the Tiroian "et", which is now the "⁊" character 1.
My question is what impact did the association of this 7-like-glyph have on the eventual placement of keyboards placing the & on Shift+7 combination?
The Wikipedia article on the QUERTY keyboard shows that the ampersand was a separate key in the bottom left of the keyboard in the original patent application drawings. The patent was filed in 1878. The Das Keyboard blog shows a Full Duplex keyboard (with separate keys for upper and lower case letters) from 1897 with no ampersand key at all. I have not yet been able to find a reference to the first keyboard to place the ampersand and 7 together. The Wiki article on the ampersand only mentions that it is usually keyed via Shift+7, but occasionally on 6 or 8 instead. Dvorak layouts appear to share similar associations between 7 and &.
So is it a coincidence? Or is there some association?
1 This looks really different in the EL&U site fontface. See the linked question or the Wikipedia article for more faithful renderings.