Thermocouples are the flame sensors in these older furnaces... a flame sensor rod is only used with much later furnaces, starting in the 1980's that have electronic controls.
Try tightening the nut that attaches the thermocouple to the gas valve another 1/4 turn or so, if that fails and you are sure the nut is quite snug, and the pilot flame is robust onto the tip of the new thermocouple, the gas valve solenoid is likely bad. The solution is to replace the gas valve, the solenoids are no longer sold separately (its a safety issue).
You could test the gas valve with this but cost is more than a new gas valve, and the valve on a late 60's furnace is well beyond the typical life span.
You can get a new gas valve at www.cozyparts.com they are Lennox specialists, they only need the furnace model number as a rule, but have all of the numbers on the gas valve itself available also.
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