This is not a T2-21 build-it article - it's an "inspirational" article on some items to highlight before actually doing them... :) Stay tuned for the next couple of T2-21 build-series articles!
First you make sure that the Divinycell H60 block is flat and has square edges. Mark the center-line and draw one side of the sponson outline viewed from top.
Then use a band-saw that you are familiar with, and has a good blade in it. Also check that the blade is straight and level. Saw a test block of something (same height as the H60 block) and check that the saw is making straight/90 deg cuts.
Carefully (slowly) saw more or less in the middle of the drawn pencil line. You should just barely see any pen-stroke on the foam core.
Sand that sawn vertical surface with a flat bar sander and 80-grip sandpaper. If you have been good in the band-saw then you should not need to sand that much.
Note, there is absolutely no time available to adjust the alignment if you notice that the parts aren't aligned. There is no looking back as soon as the plywood and ZAP'ed has met. Hold an press hard for 30 seconds.
Use a protection gloves and a BIG fan to blow away fumes! If you forget the fan - your breath will go away and your eyes will wet so you cant see... Trust me - use a good fan set on "high".
Now you use your top-view template again and mark out the other side of the sponson and repeat the process on the other vertical side...