Did you ever find a datasheet on these. I have a large quantity of them. They are sized about right for a 2W resistor, but I believe they are actually only a 1/2 watt. An early metal oxide, supposedly a tight tolerance for the time (2%).
I just finished sorting through the ones I have. A number of the boxes were label RL20. Both the boxes and the resistors appear identical to the ones labeled F20. I believe the RL20 were a newer, or replacement version of the F20. I was able to find a data sheet on the RL20 series. Link is here: http://www.ttelectronicsresistors.com/datasheets/RL.pdf
I will attach the pdf just in case the link disappers in the future.