I'm sure others will tell you better, but your gonna have issues with the mtx box in a small front wheel drive car.
I think on zetecinside.com, he said he had to cut the chassis on a mk1 fiesta for a standard bc box!

For the Ka there's myka.org and fk-oc.com and for the fiesta there is xrtwo.com

I think fitting the zetec into the Ka is pretty straight forward, there's plenty advice/guides to guide you.
Good luck