I think it's a Tecumseh Vantage 3.5 - regardless, a gasket shouldn't be a problem - but if it is you can make one out of thin cardboard (corn flake box or similar). Did mine 10+ years ago - still fine.
phil_saunders(a)bigfoot.com
Phil Saunders
September 2010
Should be a Briggs and Stratton engine on there so any Briggs dealer can get you one