That is a type "S" Bluehead engine.

...no sorry i dont know of any manufactures other than SuperTigre or Satio what the S could stand for.

Whatever it is it looks good, seems to have lots of porting going on with all the raised passages that you see on the cylinder block.

I'll keep posting stupid answers to help keep the thread on top till someone can win the prize. Just kidding, they will kick me out for that.

Good Luck