The OED gives citations (either spelling, and usages of `liefer' and `as lief') from around JA's time, and gives quotes from Thackeray, Jefferson and Coleridge. In particular, there's a citation of a dialect speaker in Mrs Gaskell's `North and South', set in Salford / Manchester. I assume Mrs Gaskell got it right, so it's North West England as well as North East.

Do you fancy Yorkshire? The Stafford family had whopping great big landholdings there, and even if they weren't connected enough to satisfy Sir Walter, the name would be reasonably common.

On a completely irrelevant point, the OED says that the original use was `had as lief', but this got transformed to `would as lief' through the wrong expansion of the phrase `I'd as lief'