Hi Paul. I am in the UK also. As long as you keep the C of G in the correct place. you can alter the design any way you choose. I have a set of the original Phil Kraft plans sent to me by a friend in Mexico. If you want to alter that shape of the vertical stabilizer, that is up to you. If you read the history of the Ugly Stik, you will find out that it was meant to be a dispensible aircraft that could be built from bits in your scrap box that could be used as flying hack to test various engines and on-board radio systems back in the 60s. As long as you don't tell the purists and the Die-Hard Phil Kraft followers, then who are you hurting. Why not have a look at the Phil Kraft Kwik Fli 3. Plans for this are easily got from the web. That is a nice streamlined aircraft and quite robust.