I'm just finishing up a windshield bag for my brother's Police Road King. He had the two itty bitty ouch thing that followed the windshied - not real useful. I tried for quite a while to figure out how to build one that followed the curve of the windscreen and decided that beaing as I was gonna end up with a crease line in the top of the flap no matter what I did with a curved one, that I would make a better sized straight one instead. Now the issue you run into is how do I mount the thing? Got my bro to do up a drawing showing all of the measurements for his road king - spacing of windscreen bolts, placement and dimensions of tach etc etc. From that I came up with a bracket that looks like a T with a reeeeally fat base on it. Now turn the T upside down and (depending on how much room you have to lower the bag) fold the base back upwards. I put a piece on the back of the bag so that the bag gets slipped down over the tab that's now pointing upward (man this is hard to explain - get into my head with me ,,, I can see it perfectly ;0)
Take a look at my page here http://mcbearcat.shawwebspace.ca/pages/ and about 2/3 down the page you'll see a pic of a partially finished bag alongside the double bag it's replacing. The two shots above that one show the attachment panel on the back as well.
When all is said and done, his windscreen bag will not follow the curve of the screen (will mount on bolts either side of center bolt) but will be lower in his field of vision and fill in the gap above the tach quite nicely. It's 11 1/2" x 3" x 4" tall.
Hope this helps
Rob