Yes u can Change the Head Cylinder to bigger one..... maximum Bore Size a 70 Chamber can have is 58.5 But u people will say how it have a maximum Bore 54 for Honda Chamber and 56 for Chonda Chambers...
Rest Picture will speak..
Now she increased her CC by 80cc means 150cc and have bigger lenght then a 70... 78mm and 70 has a lenght of 69mm... Higher Stroke, Bigger Crank means more power...