How to set output resistance of an amplifier to be 50k
I'm ignoring C3, R3 and R (2 Mohm) because they are largely unrequired.

In a common emitter/base configuration, it is the collector resistor (\$R_C\$) that sets the output impedance. In your circuit it has a value of 100 kohm and this is in parallel with the collector (acting as a constant current source) so, if the BJT were ideal, your output impedance would be 100 kohm. Bingo!

A real BJT might have a non-infinite output impedance of many tens of kohm and that, in parallel with \$R_C\$ dictates the true output impedance. However you are operating as a common base so you should definitely place a capacitor decoupler across \$R_{B2}\$ to ensure that signal feedback to the base (via the BJT's "miller" capacitor) does not ruin HF performance.

It can be quite tricky to achieve but, once you have a stable impedance at the collector, if it's below 50 kohm then you may need to pad it up to 50 kohm with a series resistor in your output line.