Some sort of comms program that supports Zmodem on the 286 end and use "sz" to send from the unix end. Zmodem has some advantages in that usually the receiving computer will auto start reception of a file when it sees a Zmodem start sequence (there's a random number handshake to stop spoofing)
The reason for recommending Zmodem is means you don't need to start the receiving process on the other computer (so no need to flip between keyboards).