I got a crush on my bike. (lowside) The lower crankcase on the right hand side was broken. Since my bike has been many hands, I have no clue which model my bike is. I don't know if it is a cb750F or just a cb750. All I know is CB750 manufactured in 1981. I do not know which model of lower crankcase I should order from ebay. Does anyone familiar with those model difference in those era. MY engine number is RC04E-2218153, Chassis No. is RC04E-2209994. ANY CLUE? Million thanks!