If the Hudson is the 763, it has a two wire IR LED. You would drive it from serial data (pin 24) out from the R4LC and hope it has enough current to handle it. This proved problematic on some installs. If you are keeping the RS2 board it already has the connections for rear light and coupler plus the IR receiver.
You can verify operation of the tender by coupling a newer TMCC engine with RS 4 or 5 and see if all functions work. If that works and the 773 doesn't you may have to swap the two wire transmitter for a 3 wire which has a built in buffer.
Pete