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Look n burner compartment and tell me if you see a model on furnace.
Wow this is going to be pretty old. Do you have a meter for checking voltage? My first step would be to find where the fan common and heat speed wire get power and checking to see if we are getting power to the motor.
A limit might kill power to burners. The only thing I can think of really if we are losing power is a bad Fan/limit. Most of these old units had a dial type fan limit that rotated around as chamber heated up. Now if that dial was bad and spring back prematurely it might kill blower.
I see you did not have the dial type.So probably not the issue.Can you trace blower wires to see where they get power and lets see if we are losing it there?