I don't know if you still have your manual so here is a copy of it.
http://www.osengines.com/manuals/50s...1fx-manual.pdf
Your engine is on pg 26.

The head gasket is extremely thin and hard to see. The drawing shows a gasket but I can't honestly say that I have ever seen mine. It may be there, or not.

You may need to go ahead and remove the piston to examine the ring. Be sure to carefully mark all parts so they go back correctly. Oiling holes in the connecting rod and such.