Whare in SoCal?
Let me clear up a few points. I have nothing against DIY projects, my input on gray scale calibration was to inform about the methods and specifications used when someone pays for a calibration and or has the equipment to accurately measure color. Customers deserve the most accurate adjustment the display is capable of.
For DIY calibration, consider an optical comparator. You can use something as simple as a photo gray card (one side is 18% the other is white) and a 6500K light (possibly a 6500K LED key chain flashlight). Display a white field on the TV, from a few feet away from the TV (possibly 6), hold up the card in front of half of the screen and shine the light on it (ambient light will affect the color). The color of the TV screen should match the color of the card.
The XBR960/910 is very capable of achieving a very flat grayscale from 10 IRE to 100 IRE. I have not experimented with the individual R, G & B Gamma adjustments because the Gray scales I have seen were accurate 10 IRE to 100 IRE in steps of 10. If the low end was good and the high end was good and there were errors in the middle, then possible individual gamma adjustment might correct that.
You will get in trouble if you try to use numerical relationships in the drives and cuts to achieve a gray scale. If the CRT was perfect there would be no reason for both Drive and Cut adjustments, however being electronic components, far from NASA specs, there are variances in the components resulting in the need for both. If you choose one color for a reference, Green is usually used, then Blue and Red are adjusted to achieve the desired White balance. There are always differences in the Drive/Cut relationships for each color. With white, it is fairly easy for the eye to see if there is too much Red or Green in the white and even at 20 IRE or below, but just how much is needed is difficult. A little too much blue just looks gray, but can be way off from 6500K. Just don't error towards Green. The color analyzer can see changes in color from just one click (for example from 14 to 15). A change in Cut, will cause a change in Drive, they are totally interactive, but not on a 1 to 1 ratio. An increase in Cut of 2 does not mean you need to change Drive by 2.
Before the acquisition of my test equipment, I did DIY calibrations on my Marquee projector. When I finally got the gray scale where I thought it was good, I was happy. When I got the equipment (guess what my first test display was), I started checking. Well, much to my surprise, it was way off, especially on the low end, below 50 IRE. It was over 10000K and the upper end was better, but around 8000K. Now that it is close to 6500K at both ends, viewing is much more pleasurable and the flesh tones are the best they have ever been. Viewing TV for so many years with 10000K to 12000K gray scales makes the transition to 6500K difficult and it takes time to get use to it.