Well that didn't take forever.....
Here's my analysis using the draw program in MS Word, not crazy precise, but within 1/8" for sure.
And here's the chart laying out how high you want to be in the centerline of your cap starting at 23.5" High going to 8".
Since your cab slants forward about 4", the "Cap" dimension starts at the top front and is the 0 mark. The "Bed" is how far back on the bed to go if you pull the tape hooked on the front of your bed it's the distance along the yellow line if you start at the front of the little block there. Height is, well, the height, in inches...the good stuff, follow those numbers and it'll give you a great curve shape. The change numbers are just there as sorta proof that I'm not out to lunch with the measurements.
If you're wondering why it's so dern high at the top front, it's because of the perspective of the photo. If I could take a side picture of a Dodge 2500 from 200 feet away with the camera at 6 feet high and in line with the bed/cab area, then it would look like you'd want. This has all the dimensions/proportions set based on your info.