That lens might cover 8x10 at portrait distances. It was meant for very high-resolution aerial work on 5" roll film, but who knows how big the image circle might actually be?
And of course, no one has ever worried about sharp corners in a portrait. Nor are darkened corners (if it doesn't cover completely) usually an issue.
And as an aside, my friends and colleagues who shoot tintype prefer 6"x8" plates.
Can you tell that I'm acting as an enabler here? Go for it!