Icom IC-746 (IC 746 IC746) transceiver mods reviews software and diagrams

There is the interface. This one shows a 5 radio hookup -- just use the one jack if that is all you want. The inductors are all RFI suppressors, you can skip them if you want (L1, L2, L3, L4, as well as C5). The important parts are the five 22uF electrolytics, the Max232 IC and the 7805 regulator.

Easy to build -- works fine.