OK...so as the current owner its your responsibility, legally, to inform DVLA of the changes. When you do that, I'm sure they will say its been substantially modified and therefore not MOT exempt. Don't forget that if you don't inform DVLA, your insurance may possibly be invalid.
Edit.....it's no agro getting an MOT anyway, its got to be road worthy and safe at all times, so the need to have an annual MOT should be of no issue at all.