Is your crank puley degreed and can you see it?
If so remove one valve cover. Then pick one cylinders intake exhaust valves.
Hand crank slowly until you note the intake to just begin to open. Note how many degrees before top dead center it is (TDC).
Continue turning (did I mention it must turn in correct direction) until it just closes. Note how many degrees after TDC. Do same for the exhaust. How many degrees were the intake and exhaust valves open for?
Also note, this will not be accurate due to valve lash but can get you close...