Victa used a Tecumseh as a four stroke option on that base which obviously fits without clearance issues. That and perhaps Honda and the V40 must have been the four stroke options on offer.
IIRC the Briggs used on the early thumb latch base during the full crank two stroke era, had an exhaust that directed the gases side ways away from the rear of the base. Many owners or mower service shops must have just fitted the standard muffler when it needed replacement, causing the black coating.
