Not sure. But you can buy a Prolinx Gateway that can act as a protocol converter. IEC 60870-5-104 can be converted to Allen Bradley DF1, Ethernet I/P etc. So might be a better option.
Siemens S7 300/400 using standard hardware. A Company located in Norway have done a software solution with function blocks. I have done a project with 101 protocol using these function blocks and I know they also have a solution for 104 protocol. I have forget the name of the company but I will do some searching and come back with it.