I think that pattern is an unholy mess. Here's my suggestion: grab a clean piece of paper. Draw a vertical line on the right side (CF, as in the existing pattern). Place three points on that line, for the upper edge, bust line, and lower edge (their N, F (except they don't use it,they drop from S to T) and O points) based on your taste - eyeballing on myself, 2 1/2 inches between N and newF, and also newF and O, (total height 5") but it depends on your shape and modesty. Draw lines at right angles out from there, to half your bust (as per their D-F measurement), and draw another vertical line (like their B-C) for centre back. So you'll have an E, a D (or newD) and a new point, extension of the O-P line. Draw a vertical side-seam line (like their L-K-P), about 1/4 of your upper bust (40", right?, so 10") from CB. Drop the upper back edge about an inch - 1 1/2 (eyeballing/taste again). Go straight across from the dropped E, start to curve up around the L, so you'll have a new dropped L point on the side seam line.
Now ideally you'll have your bust point to bust point measurement (across your chest) otherwise it's just under 1/4 of your total bust. Measure half of that, I'd expect about 4" from CF (N - newF - O) and draw another vertical for the bust point. Using your actual measurements (45" bust, 40" high bust), mark 1 1/4" on each side of the bust vertical on the N-E line, and draw in the X like the original pattern. Now the upper edge (once the X is sewn/pivoted) should be (half) your upper bust measurement, or a little looser, adjust to taste.
The lower edge needs to match your underbust, 38". If the X isn't centred, you'll need to measure how long the underbust line is now with the X dart out, but if you've gone with the 2 1/2, 2 1/2, that lower edge would now be 20" like the upper edge, and it needs to be 19". Go to the side seam (L-K-P) and draw points on either side of P to take out the extra inch (whether it's best balanced or not depends a bit on your figure). Draw straight lines from these points up to the dropped L point to make side seams.
That should be it - as per the original (and all pattern drafting) draw in smooth curves (particularly where the two new points on either side of P are joined to make the underarm seam, and also around L/new L), and make a mockup.
I hope the relationship between your measurements and style preferences, and the pattern, is now clear enough that you can figure out where to adjust for fit and taste.
If you pivot the side seam out (along with the upper part of the X) to make a single piece as in the original, I can't guarantee the CB will be exactly on grain but based on your measurements it's going to look a lot better than what you've got!
no subject
So you'll have an E, a D (or newD) and a new point, extension of the O-P line. Draw a vertical side-seam line (like their L-K-P), about 1/4 of your upper bust (40", right?, so 10") from CB. Drop the upper back edge about an inch - 1 1/2 (eyeballing/taste again). Go straight across from the dropped E, start to curve up around the L, so you'll have a new dropped L point on the side seam line.
Now ideally you'll have your bust point to bust point measurement (across your chest) otherwise it's just under 1/4 of your total bust. Measure half of that, I'd expect about 4" from CF (N - newF - O) and draw another vertical for the bust point. Using your actual measurements (45" bust, 40" high bust), mark 1 1/4" on each side of the bust vertical on the N-E line, and draw in the X like the original pattern. Now the upper edge (once the X is sewn/pivoted) should be (half) your upper bust measurement, or a little looser, adjust to taste.
The lower edge needs to match your underbust, 38". If the X isn't centred, you'll need to measure how long the underbust line is now with the X dart out, but if you've gone with the 2 1/2, 2 1/2, that lower edge would now be 20" like the upper edge, and it needs to be 19". Go to the side seam (L-K-P) and draw points on either side of P to take out the extra inch (whether it's best balanced or not depends a bit on your figure). Draw straight lines from these points up to the dropped L point to make side seams.
That should be it - as per the original (and all pattern drafting) draw in smooth curves (particularly where the two new points on either side of P are joined to make the underarm seam, and also around L/new L), and make a mockup.
I hope the relationship between your measurements and style preferences, and the pattern, is now clear enough that you can figure out where to adjust for fit and taste.
If you pivot the side seam out (along with the upper part of the X) to make a single piece as in the original, I can't guarantee the CB will be exactly on grain but based on your measurements it's going to look a lot better than what you've got!