Vince,
I asked the same question, and got some very helpfull information. From memory the blue is 2 inches and the red is 5/16", spaced 5/16" away. Look through my post on JPN colours and there are links to an actuall original tank, from that it lok like you can reference the stripes from the fron of the tank at the top, by looking at the photo, the red 5/16" stripe starts 5/16" from the edge of the flange near the steering head. also note the blue line, does not go down into the recess of the fuel tank filler, at the front.
Will have to compare note when you start painting?
Cheers Richard