I am researching how the bows of the Essex class carriers changed from their entry into the fleet in 1943 through their long history, and have come across some recent pictures during their modernization periods that may provide a better understanding of how the updating was done.
Short Hull / Long Hull
As originally configured, the Essex class aircraft carriers had a rounded bow as shown at far left above. 
During construction, most of the later units of the class had the bow reshaped into a "clipper bow" which was flared forward and to the side to accommodate the second 40 mm quadruple mount antiaircraft gun as shown in the drawings in my 1997 book Essex Class Carriers in action. The photo of the Shangri La (CV-38) at left is one of the few that seems to show a bit of a jog in the main deck, and a change in the hull plating where the bow lines were reshaped.
SCB-27A/C
During the initial round of postwar modernization, six of the "short-hull" units were brought up to SCB-27A or -27C standards, and in each case their bows were altered to the "long hull" form.
After doing some research, I think how that was accomplished is a little clearer. These two photos shown the Essex (CV-9) beginning her modernization in April 1949. Oddly, the sides of her flight deck forward have been removed, which doesn't seem to make sense, since the flight deck remained after the conversion.
But I was looking at similar photos of the Lexington's modernization at Puget Sound five years later and the pieces fell into place.
These two photos, taken in April and June of 1954 show a short-hull Essex being reshaped into a "long-hull" prior to also receiving a hurricane bow, since Lexington went straight from her World War II confirguration into a SCB-125 one. In other words, she missed the middle stage of the top photo, and went straight to the third photo.
In the first photo, "No. 1 and No. 2 sections of new bow" are in the foreground. The structure behind is the third "bent" supporting the flight deck - everything forward of it has been removed, and the entire bow forward of about the first bent has been sliced off and a new section of bow with the clipper lines is being prepared for attaching.
For purposes of illustration, the attached photo of the Oriskany model shows the three "bents" on a long-hull ship.
Here's the interesting part. 
The next photo, taken two months later, shows the new hull section (with a hawsehole, I note) attached and notes "installation of two of the three flight deck sections removed earlier in the conversion. And now we see bents # 1 and 2 reattached to bent #3 and to the forecastle - essentially the section remaining on Essex in the photos above. And this is when I noticed that the pictures of the Essex showed a railing being placed separating the forward section of the flight and gallery decks - it was because they were about to be removed.
But this shows how far back into the hull and superstructure they went in the "short-hull" ships to reshape the bow lines in the SCB-27A/C modernizations, and for the two "short-hull" ships that did their -27C and -125 at the same time, Lexington and Bon Homme Richard.
In case you're interested, 
the hurricane bow itself was delivered on a truck and mounted on the ship by crane.
SCB-125
Did the bows have to be cut back this far in the SCB-125 conversions that added hurricane bows? No.
As the attached photo of Ticonderoga shows, while the technique was similar, the section of bow that had to be cut back was far smaller, and didn't require removal of any of the flight deck supports. This photo of Shangri La shows only half removed, and then during the bow rebuild. 
But why was any removed at all? I had assumed that the clipper bows were just faired up into the new hurricane bows.
The "clipper bows" caused excessive slamming in service, with the Ticonderoga buckling her main deck during a passage around Cape Horn, causing major damage. This reinforced the need for hurricane bows, but also resulted in the existing bows being reshaped slightly to offer less resistance to the waves in heavy seas.
As this comparison of the Oriskany's forecastle after her SCB-125 modernization to a long hull forecastle kit part shows, the corners of the bow were rounded somewhat, which made the final hurricane bows less likely to cause unwanted slamming.
