Shortline Sammie is spot-on. The setup is built by Griswold, although the parts commonly used are as follows:

Gate mechanism--Griswold "EM" class gate, known colloquially as a "Griswold Pedestal Base" in the rail community. US&S was going the exact opposite direction in this time with their AL-70 lightweight mechanisms, although they also were cataloging the Model 75 mech.
Flashers--Griswold "Type B" flashers. Of note is that these would have been one of the few back-mounted flasher setups in common use.
Bell--Griswold Type 2B mechanical, with full-top rainshield.


A re-creation of a full-fledged Griswold setup in OpenRails. The gates are my own models, derived from blueprints put up by the Niles Canyon signalling team. Their organization has two in daily operation at Brightside with the older "A-frame" crossing gates.

These setups were often modified after the fact, receiving larger 12" flashers through upgrades such as O Street in Sacramento.

Also of note is that another builder known as RACO also produced these mechanisms under license before Griswold, RACO, and Safetran merged in the 1970s / 1980s. These can be distinguished from Griswold setups by the general crossing arrangement--i.e. whether the flashers closer in design with modern Safetran lights like RACO's more spartan design or have the rail-in-circle logo--and by up-close inspection for a RACO builder's plate (also with the rail-in-circle logo) near the mounting point of the gate arm.

I can't provide as much detail since I'm not as experienced in the matter but some of the folks over at RXRSignals.net probably know more than I do. Nonetheless I hope this is of some help!