get a nice big can of thinners bud from ur local parts shop ,

strip it down , soak all ur rockers valves ect and grab a stiff bristled painbrush sit it in a bucket big enough to fit it in and soak it then go at it mate ,

nowt like a but of graft lol ,

even eaiser if u got a mini wire brush ofr the dremmel to get in nooks and crannies

hope this helps ya mate