Mixer spurs and IF output filters
Here is one way to do it:

Terminate the mixer into a common-base (or common-gate) amplifier, using a resistor in series with the input to increase the input impedance to 50 Ohms. The output of this amplifier can drive your filter. Increase the bias current if you need less distortion. 

Instead of terminating L1 and C1 to ground, connect them to the positive supply voltage. Add a 50 Ohm resistor in parallel with L1 and C1 to provide a 50 Ohm output impedance. The current to feed the collector of the common-base amplifier will go through the inductor. If you increase the filter input impedance (and the collector resistor) to a value above 50 Ohms, there will be gain. The value of this gain can be adjusted to maximize dynamic range, improve sensitivity, or reduce distortion. The advantage of having L1 and C1 in parallel with the resistor is that the resistor value can be made larger without reducing the collector voltage.

Usually, the worst problem with an amplifier in this position is that the second-harmonic distortion of the amplifier will cause a signal at 100k to be converted to 200k, which is in your passband. A 100kHz notch filter on the input side of the amplifier will help get rid of this.

To stabilize the amplifier, put a ferrite bead or 10 Ohm resistor between the base terminal and ground.