The KL ECU would need to be wired into the car while the KF is already there. The timing should be almost identical but with more air through the AFM the ECU will add more fuel to compensate when the O2 sensor cuts in the ECU will maintain the air/fuel ratio.
I know someone who did this to a Eunos 30X. K8 out KL in. Instant 60-70% power increase without any visual difference
I've only just thought about the crank angle sensor and harmonic balancer. The KF front housing may need to be swaped or the KL unit modified. They are probably identical but it would be the ideal time to investigate making the sensor somewhat adjustable.