The only Tool we are aware of is asc3270 from Advanced Software Concepts,
which offers 3270 terminal emulation via the CommToolBox. Currently, it
only supports telnet connections over TCP/IP using their TCP/IP connection
Tool called TCPack.
Since you already have coax to a 3174 controller, SNA*ps is a better
solution since it provides better keyboard mapping and terminal emulation.
If you insist on using MacTerminal, you will have to wait for the SNA
connection Tool from Advanced Software Concepts.
Other 3270 connection solutions are also available in the Technical Info
Library. Search using keyword "Macintosh and 3270."
On AppleLink, you can find contact information for the various vendors by
clicking the Library Index button to view the folder structure in the Tech
Info Library. An alphabetic listing of vendors is in the Third Party
Company Directory folder.