So the starter must magically drive the crankshaft to start the engine? A bump start engine cannot have an electric starter attached to the rear of the engine without first changing the crankshaft to add the SG drive pin that the starter assembly will drive. So at the VERY least, you're tracking down a crankshaft for an engine that may never have come with the pullstart crank.
Lets see some detailed instructions and diagrams how your system installs. I am still not confident that it's going to work without extravagant parts sourcing.