if there is no rear seats then the rear seat belts need to be taken out and the insurance side of thing i just told them it had interior changes and they are fine with it lol
I had a zetec s b4 i got my GT everything was stipped out of it i used to get pulled over by traffic cops and normal old bill and they never said anything about it....So you should be fine mate
Best thing to do is get a TD04 or TD05 kit and that way seats wount make much diference mate. Anytime guards will stop you its just hassle that you can do without. (specialy if you cought in a cruise or even racing) Imagine doing 130 in 120 zone and guard pulls u over bad enought you are driving a glanza then he sees the back is stripped out he will eat you alive at the side of the road. Myself I try to have things on the outside as normal looking as possible saves alot of hassle.Thats my advice to you.