Be very careful make sure it is set deep in socket. or you can strip them.
Let me look I may have a good piston for the 670. Give me a call If you don't want to mess with it.
Shopped at Ace hardware for a 'T' handle but a set of metric is 25+. Wait till the streets are cleared of snow before I venture to Sears.
New pistons w/rings on evilbay run 30-45 USD, so that isn't any problem.
Top end kit is around the 150 mark. So it all depends on the cylinder condition.