RE: Free to good home receiver and 3in1
I don't know if the Tx will work with the 4-in-1 but there's no reason that it shouldn't if you have the correct crystals for the Tx and the receiver in the 4-in-1.
Also, the 3-in-1 will not work in a CX/2 because it uses different mixing than the CP and needs a bigger MOSFET for the second motor. The 3-in-1 should have an ESC for the tail motor of a CP but that takes less current than a CX motor so a CX motor will most likely burn out your 3-in-1.
If you are giving things away, I would like the 6100e and could use the 3-in-1 if it's not broken. Send me a PM and let me know!