I figured out a way to find the valve sizes, for the inlet and exhaust.
I had to find what the mean piston speed was then. Which to find that i had to find the RPS @ max then multiply that by the stroke length then multiply that by 2.
That gave me 20.14 m/s
Then I had to plug that information into a excel spreadsheet that gave me the inlet/exhaust diameters for the valve sizes.
n.b. My lecturer helped me in making the excel spreadsheet to aid me in compiling all of the formulas needed into the spreadsheet.