I just checked the B13 FSM, and the ECU might work the B14 tach since it uses a speed sensor (not a cable). It depends what signal the B13 ECU sends out, AC or DC (the B14 tach needs a DC voltage). You'll need the pinouts for the B13 and B14 clusters. It's not likely the connectors are the same so you'll have to splice the B14 connector onto the B13 cable (unless you want to try to install the B13 cluster).
Lew