1970 Briggs & Stratton 9hp

Picked up a 'winter project' to keep me busy!
Initially used to power a beet cleaner but then sat unused fo many years in a barn. Looks worse (really!) than it is, turned over freely but no compression. Drive end has a 6:1 gearbox fitted.
Bore has about 003in of wear with the piston measuring 012in down on nominal and broken ring! Exhaust valve was not closing properly due to an enormous amount of carbon in the port.
It is one of their Spin Easy designs which according to what I have read involves an extra lump on the cam to hold a valve open in advance of it's normal function making it easier to turn over.
However now it's all stripped apart I can't seen anything other than a standard looking camshaft?
Anyone experienced these?

Alan