Head to head, fist to fist, 12 rounds if required, the version of Gibbons who faced Dempsey versus the version of Briggs who faced Lewis.
Case Study #2. Briggs heavyweight victories include Liakhovich, Mercer, old Foreman Gibbons heavyweight victories include, almost exclusively and exhaustively, a sick Miske in his third to last fight. Classicist pick? Gibbons, of course.
No way in hell that an unskilled bum like Briggs would even land solidly enough on Gibbons to knock him out. Depending on how defensive Gibbons plays it it could go UD either way.