Personally I would not try and touch up the red zone, I think you might be disappointed and then start looking for an alternative. To search, make sure you go back to the main home page for the forum. While its not obvious, the searches go from what ever thread your in, rather then the entire forum, at least that's my experience. Lots of posts associated with these search terms "gauge face".
Here are a couple of good ones:
http://forums.sohc4.net/index.php?topic=88015.msg989242#msg989242http://www.cb750faces.com/webshop.phphttp://forums.sohc4.net/index.php?topic=57350.msg621381#msg621381Lots of people here are downloading templates, printing them on high quality printer and then gluing them to the existing faceplace.
Relative to taking the ring off to open the gauge: Patience of a camel is recommended! I took a file and sharpened the edge of the paint key. In some cases I had to use a knife blade to slightly spread the lip in order to have the key fit in the gap. What I did notice is the rim is somewhat loose on the gauge. In other words, if you push the rim towards your working area from behind you will open a gap. Also when you push up on the ring towards your work area you will be able to bite better with the key.
Obviously you should be working on the ring from the backside of the gauge in order to hid your work once reassembled.
I did not have to fully open/spread the ring lip as the top rim of the gauge is easily shifted once you start loosening the lip. I probably went around the lip twice with the key and spread the lip a little further each time. I then pushed the lip towards the work area and was able to pry up on the rim of the top of the gauge and it popped right off.
Popping the needle off took allot more pressure then I thought it would. I dripped penetrating oil onto the needle/axle interface and let it sit for a few mins. I used the fork method but was concerned about the lower portion of the fork pressing down on the painted face. I put a Popsicle stick under the bottom edge of the fork to protect the painted area. Mind you I was wanting to reuse these gauge face plates in my case.
I have not put anything back together yet. In another post I had asked for recommendations relative to cleaning and painting the removed gauge face plates with say a flat clear paint to kind of blend the various shinny or oxidized areas on the gauge face to be more uniform. I got a recommendation from a member for a flat clear paint used for models, hobby store again.
Again I think my case is a little more unique in that I purchased "used" gauges that had face plates in much better condition then my own and I am swapping them!