I don't have a link for you but the oil is pretty simple stuff.
the fill cap is black plastic (if you say you overfilled it you probably know where this is already) just below the fill cap is a metal bolt sticking straight out of the engine block right at the bottom, this is the oil drain. open this and the oil comes out.
for reference the correct oil level is to fill up the to top of the fill hole when the engine is level, so there should be oil just ready to come back out of the fill neck were you to add any more.
don't check the oil when the engine is warm, nor should you top the oil up when it is warm.
try looking for the manual for the honda GX-50 or GXH-50 engine as that is the engine Huasheng cloned, all instructions are interchangable between the two.
good luck