Hi Bob, no problem...
The last straight piece of the shelves, the one extending from 246-5/8 to the stern, is to be lengthened by 24" for the 28' boat. Noting that the shelves DO taper inward over this same stretch, it is perhaps noticeable that the shelves will taper inward too much versus the transom width. This is OK. That is what I meant by wiggle room on the shelf molds in the construction manual. You of course will adjust the shelves in their molds so that they land correctly at the outer edges of the transom as they should.
So, for lofting as in Sheet 002C-Alt, the lofting for the 28' boat is exactly as shown in that drawing out to the 246-5/8" station line. The end of the wood, shown at 325" for the 26' boat is 43-1/2" as shown in that drawing ...this is for matching the transom width. For the 28' boat, you will want the 43-1/2" width to occur at 349" (that's 325" plus 24"). Clear as mud? Life would've been easier if there were no stern taper in this boat...
Brian
PS: You could alternatively add all the extra length to the middle piece of shelves since that's a straight run and that would work fine as well, or you could add 12" to each of the last two pieces, but that might confuse things further.