We need a zero cross circuit which gives a falling edge 430us +/-50us before the zero cross. The attached is the best we can come up with. Do you have better?
The advantage of the Type II PD being edge-sensitive (dual D FF) makes it both a phase+frequency detector to have a capture range equal to the entire range of the VCO. This disadvantage is a dead-zone from latency.
Basic law of capacitor behavior: series cap advances sinewave current.
Values in the simulation work for 500 Hz. Voltage across the anti-parallel diodes crosses zero at a point 450 uSec preceding the source. Experimentation will reveal what RC values work at other frequencies.