Lawn Boy manufactured their own 2 cycle engines from 1955
until Toro bought them out in the late eighties.

Are the cylinder fins round or square? Does it have head bolts (removable head)? Round fins would be the 'F' engine. Square fins with one-piece jug is the 'V' engine. Both have iron sleeve and roller bearings.

Outboard Marine Corporation, Or better known as OMC.

A '30 yr old' Silver Series is not an 'older' Lawn-Boy made by OMC (Ole Evinrude). It is a late Lawn-Boy with a Lawn-Boy engine, either prior to or after the purchase by Toro. Either an 'F' or a 'V'.

Thanks all. It's a relative's mower, so I'll take a closer look at it next time I visit.