I have the brochure, it says the W6 has a 222cc, 6hp, Tecumseh 4 stroke engine. The W6 was recoil start and the W6E was electric start.
The W8 model had a 314cc, 8hp, Briggs and Stratton 4 stroke engine with electric start.
However, this isn’t to say that the W6 was never available with a Briggs engine at some point. I’d be tempted to install a Briggs engine in any case if the current engine proves beyond repair.