Hans and JZ,
I interpreted the mixer behavior in the context of real life situation where the LO and RX freq are fixed. We have a target signal at the RX freq, and unwanted interference at a certain offset from the RX freq. I think the rejection of the unwanted interference is likely better than shown in the RF sweep plot because the mixer presents a lower impedance at the interferer's frequency depending on how large the offset is.
Deliciously rich it is. The RX sweep plot changes with and without the functioning final transistors in place.
Ryuji Suzuki AB1WX