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There are numerous possible problem items that would cause the gas valve not to open. I will do my best to list them. First off, Fraser-Johnston was not a big name in my area but almost every furnace from that era worked the same and had similar parts.

#1 The pilot is lit since it has it's own gas supply and is not affected by a control malfunction. That pilot heats a thermocouple that is supposed to supply a small voltage to the safety pilot/gas regulator. (See that small line at the bottom of the device with the red cap). If the thermocouple does not produce the correct amount of electricity that device will not operate, and gas will not flow.

#2 In the 2nd set of pictures in your 6:21am post, that device in pictures #2 & #3 at the top right with the wiring attached, is a 24 volt transformer that provides voltage to allow the furnace to operate. The voltage leaves the transformer and flows through the thermostat, limit devices, and the gas valve and returns to that transformer to complete the circuit allowing the furnace to operate.

#3 In order to trouble shoot your furnace you need a volt meter to see where the voltage is being stopped and not allowing it to complete the circuit. If there is 24volts on the gas valve and it does not open it may be the problem. Any descent ist year apprentice could trouble shoot your furnace and see what device is at fault. The biggest problem is that a lot of the young service guys have not seen a set-up like yours. They are too young not an old retired guy like me.

#4 What you need to find is an older gent that has experience with older equipment. If the problem is the gas valve a new type combination valve could be installed but there are other devices that may be malfunctioning. If the chamber in that furnace is not cracked or deteriorated then fixing the furnace is your best and cheapest option. Go find a good and reputable HVAC company that wants to fix that furnace and not just replace it.