First usages, in print
Whopper (large) - A cant term, in Grose' Vulgar Dictionary, 1785; a large man or large woman.
Marryat, in a novel about Nelson, speaks of him passing up some whoppers in favor of a four-master.

Whopper (lie) Nairne, Poems, 1791; Some do affirm- sure, 'tis a whopper! / Thou'rt silver plated on copper. By late 18th c., the word was regularly used for a lie.

Guest Neill D.- many song sheets about murder at the Bodleian Library. I haven't gone through them, but there may be Ratcliffe murder in some of them.