My '71 Caravel
was reasonably well sealed in it's original installation but I don't know what they did in '65. On my '71, there was a screened vent in the floor with another screened vent hole cut below it in the bellypan. Then above the unit, there was a curved plastic vent about 20" wide and 3" deep that went up to the exterior refrigerator roof vent. That took both the combustion gasses and heat to the exterior. The refrigerator was set below the kitchen counter, and was more or less sealed from the interior so the air could circulate only through the back of the refrigerator compartment. It was not "caulk sealed" however, just reasonably tight.
When the gas flame burns, it should produce CO2 and water vapor (plus a few other things) with no CO. CO comes from the incomplete combustion of gas. As long as there is enough oxygen very little or no CO is produced. With low oxygen, CO is a very possible product, but not with enough oxygen. CO is dangerous, CO2 not very much, except in very high quantities.
When you cook with gas, open flame, there is virtually no CO produced, but again, only CO2 and water vapor, neither being dangerous in small amounts from cooking. The refrigerator gas flame is pretty small to begin with, and with some ventilation should be no problem. However, some, not none....
I hope this helps with your understanding of the venting needed.