There's a spec sheet at http://www.mymowerparts.com/pdf/Briggs-&-Stratton-Spec-Charts/ which says that the basic model series for the 28/31 cu in Intek singles are 28S700 and 311700, FWIW.

The parts lists that site has for download do list the Type Numbers that were used, within those model series.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."