On my vintage TS-430S I dug into the circuit boards and added shielded cables from the IF Unit board to an external MiniDIN 6 Pin connector much like the data connector on later model transceivers.
TX Audio from IF Unit,Connector 5, pin 3 to MiniDIN6 pin 1
PTT from IF Unit,Connector 11, Pin 3 to MiniDIN6 pin 3
RX Audio from IF Unit, Connector 4, pin 4 to MiniDIN6 Pin 4
Shields and ground to MiniDIN6 Pin 2
At the time I connected this MiniDIN connector via a multi-conductor cable to a transformer isolated and level adjusted prototype board (on RadioShack 274-150) of my design that also had a data operated transmit (DOX) circuit of my design on it. My external circuit board then had 3.5 mm (1/8") audio cables to the line input and output connectors on my computer. Speaker and microphone connectors on the computer could also be used with appropriate level adjustments.
I see no reason why a SignaLink USB or equivalent interface would not work as well -- or maybe better. I used this analog interface on 20m with PSK31 using the TS-430S but have not used it with other modes except for MT63-2KL on 2m. I now use a SignaLink USB interface on both VHF and HF on later model transceivers with a 6 pin data port.