cortina mark 2 identification

Hmm Sounds like you've already consulted this site

http://www.cortina-mk1.com/identify.php#mk2

Tommy Sandham's site does refer to a 75 as follows: 75 = Cortina 4-door DeLuxe, column change

http://freespace.virgin.net/tommy.sandham/chassis2.htm

Yours a 4 door column change?

thanks i had a look at that site but i still can not find out why it
has a ja engine

yeah, CN is definitely a GT motor, sounds to me like someone has put a GT motor into the car at some stage. Most of the Ford cars have matching chassis and engine numbers from the factory, with the exception of a few, the Lotus mk1 escort being one of them.