.Please tell me the impedance of LO input at 10MHz and also the value of the components(C3,C4,C5,L5) required for the reactive matching at this frequency
When you start getting down to such low frequencies, the LO input impedance is mostly characterized by the internal resistors shown in Figure 7 on page 17 of the datasheet. For this part, the LO input impedance at 10MHz is going to be in the neighborhood of 160Ω.
It can be difficult to get a reactive match at 10MHz, so we would typically just use a resistive match with a DC block as is shown in Figures 21 and 22 on pages 24 and 25 of the datasheet. Using 160Ω for the resistor will give you roughly 10dB return loss at 10MHz. You can decrease the resistor's value to improve the match, if necessary. Note that you may need to increase the LO drive slightly to maintain the performance since some signal power will be lost in the resistor. You can play with your LO drive level to see what gives you the performance you require.