So what scale will a corrected build end up? Well, as usual there are several ways to answer this. A quick measurement of the flight deck (19.6") - calculated against the overall length (LOA), as listed by NavSource (899' for USS Yorktown) - indicates an actual kit scale of exactly 1/550 to begin with, but with our bow correction (+1.01" forward), that scale increases to 1/523.
Now the above is based on length overall, which can be dicey because of minor changes - for example a bridle-catcher here, or a gun tub there, etc. - so that the far better way of pinning down scale based on length is to consider the waterline length. Indeed, Navsource lists the waterline length (WL) for all Essexes as unchanged - from 820' as-built - right through their radical conversions even to the SCB-125 fits. Based on this dimension, the Revell kit starts out at 1/538 scale, but again with our bow correction ends up at 1/510.
Meantime, as I've noted earlier a key consideration for most hull conversions is actually the beam - again, always measured at the waterline - and here the original Revell kit is erring in the other direction; with a waterline beam (1.95") scaling out to 1/622! Now this is for the beam an SCB-125 Essex - 101' in real life - which was significantly wider than the as-built WL beam of 93'. (I think Revell must have used this earlier beam measurement in designing their mold, as this would calculate out to 1/572 scale - which is at least back in the general ballpark with their target of 1/542.)
In any case, the beam of the Revell kit needs to be widened (even before our bow correction) to match the scale based on length. With our bow correction, we are again faced with a choice of target scales: 1/523 based on LOA or 1/510 based on LWL. In this case I recommend splitting the difference - taking the average of the two - which comes out to 1/517 scale. Thus, I calculate and recommend that the keel requires the insertion of a 0.40" spacer plate along the centerline of the (single-piece) hull; leaving the ends attached so they will naturally taper back together. I know this is a lot of plastic to jam in there. I have successfully inserted, on this very kit hull, a 0.30" spreader before - so I know that at least that much can be done. If more than 0.30" proves unfeasible (the other option being to build out the hull sides, as was done in the actual refits), then the resulting scale, based on the beam, will come out to 1/539.
So, there you have it - the scale to which the Revell angled-deck Essex should be corrected is: 1/510 based on LWL; 1/523 based on LOA; or 1/517 based on the beam - take your pick - unless you can't swing the latter and have to settle for a beam of 1/539! Is the above about as clear as mud now?