Needed to be removed: turtle deck skin all the way to the tail, the upper section of all three turtle deck bulkheads, modifying the bottom of your vertical stabilizer and tail intersection fairing, removing your installed canopy side rails, windshield and windshield roll bar, boot cowl skin that intersects with the new tip over canopy and and front glareshield. Then you’ll need to install all the parts you just removed with the new replacements parts, including welding the new roll over bar to your existing front seatback support. That’s all before starting the fiberglass parts for the fastback canopy.
Don‘t get me wrong, I love the Showplanes Fastback mod - I built one, and it’s beautiful. But I built it as an original part of my RV8 build. I think retrofitting the Showplanes mod on an existing flying RV8 will be at least twice as much work, and require very good attention to detail to make it all fit right. Anything is doable, but make sure you know what you are getting yourself in to.