The motion will not be pure sinusoidal, the small angles of the connecting rod will skew the output motion away from a pure sine wave. Why don't you graphically lay out the mechanism and plot the output motion vs. crank angle. From that you should be able to determine if the motion will still work for you. I can tell you that if you connect the con rod to the lever and the crank with scotch yokes, the result will be sinusoidal. Or, for a more rigorous analysis, write the equation of motion for the output, only a bit more complicated than a graphical analysis, but still simple geometry.