Hate to say it, but you need to pull it down again and not assume anything. You are missing something simple. In fact you shouldn't even have ran it, you should have squared away that no kickstart problem first.
The overflow deal is overheating/air lock related. You have a bubble of air trapped in the cooling system that expands when it gets hot or you have a blown head gasket that is allowing the cooling system to pressurize excessively. Since you say it won't stop, I would tend towards the failed head gasket.
Net:
Tear it down completely and do it right, paying close attention to spacers, shims, and washers