The 1770-KF3 converts from DF1 to DH485 protocol.
The 1761-NET-AIC (AIC+) converts from RS-232 to RS-485 signalling. It does not convert protocols. You can run ASCII, DF1 Half Duplex, Modbus, or DH-485 over an AIC+.
DF1 can be transmitted over modems because it is asynchronous, but DH485 cannot because it it relies on precise timing. That's why there are devices like the 1770-KF3 and 1747-KE module.
There are some 3rd party DF1/DH485 converters on the market but I cannot attest to their functionality.