It's the standard, "leftie loosey, righty-tighty" thread.
Pull the shaft out, get some small vise-grips or something that can REALLY hold the shaft, and then use another pair of pliers to remove the knob. Use a paper towel to help prevent scratching the chrome. If you want, try spraying a little JB Blaster into that knob beforehand.
I offered quartz conversions for clocks for awhile. These were typically very easy to do and I enjoyed it. However I got out of it for three reasons: (1) the price to me from ISI was the same price as for any customer, so I had very little profit margin. They offered dealer discounts, but only if purchased in bulk. I might have eventually done 100 clocks, but not 100 1964 Thunderbirds in a row. (2) I could only convert certain clocks made by Borg, 1963 and later. ISI would not offer training, or any support of any kind, for other models. So for customers it was a pot-shot as to whether I could do their clock. (3) My main service is radios -- and demand has been so strong that I simply stopped offering clock service.
That being said, I highly recommend these conversions. The clock movements are wonderful. With just a small amount of skill and patience you can purchase a movement and install it yourself.