I never used the set you're referring to, but did use separate N.J. International signals and crossing gates on a club layout.
The signals were installed and used a few months before I decided to add the crossing gates. Fortunately, the Grade Crossing Pro circuit boards I used for the signals also have a crossing gate output that drives a Tortoise slow-motion switch motor, which is what you use to lower and raise the gates.
I don't remember where I purchased the necessary linkages, but crossing gates require a quite complicated system of cables and cams between the gates and the Tortoise. The gates were free-moving but did not have the necessary linkage, so I had to experiment with that aspect of the installation. What I wound up doing was drilling a small hole in the gate counterweight and running a very small music wire linkage down through the layout to the linkage and then working from there back to the Tortoise.
P.S. -- I just found the linkage set in the Walthers catalog -- it's made by Circuitron and is Walthers catalog number 800-8100, priced at $10.95. An extra cable and actuator, catalog number 800-8101, is priced at $5.95, and is necessary if you want to control two gates with one Tortoise.