There's a ON1102 photo interrupter "home detector" on the left side and a carriage return position switch on the right side.

Sure, we can keep it at 8.5.

For printshop, if I set the left edge to be -32 pixels it will fit neatly centered within the borders. (I think that's what it was when I was experimenting.) However, negative offsets mean that normal text gets started off the left side page so you lose the first couple of characters.

So you could have a config option to set the left edge offset.