I think the answer is no, as far as I know, the aluminum-deck Lawn Boy mowers were two-strokes. I've seen a lot of them (own one, always looking for more :biggrin
and I can't remember any four-strokes.
Maybe Hankthecrank could give you a definitive answer -- he would know if anybody would.
If you want a four-stroke mower with an alloy deck that will last forever, plenty of other brands are out there. My Jacobsen is Briggs-powered -- excellent deck and wheels, so-so engine. It doesn't do nearly as well as the Lawn Boy (which is also lighter) in thick grass.