The easiest way would be to put a sprocket on your briggs ratchet thing, with a chain wraped around it..
One end of the chain has a spring pulling the system back home, the other end is attactched to your kickstart lever..
I'd make a strong steel plate, that bolts down underneath the engine, which your kicker arm all works off from.. If you put that kind of a load on the thin steel shrouds, it twists them all to hell...
But a base with kicker arm, hooked to a chain, wrapped over a sprocket on your starter sprag, would work very well, and is an easy build...
Look up a kickstart Briggs and Stratton Model A :thumbsup: