Taken from another forum
Originally Posted by Stixy
September 84 will have the narrow tunnel without the sliding mounts , but unless your going A4ld or 4x4 shouldnt it be a problem , Type 9 will fit straight in MT75 from memory will need blocks between the g/box mount and the brackets on floor .
I will see if i have any pictures but its been about 12 years since i put an MT75 in a mk1 ( for sombody else ) and it was pre digi camera days so may take a while
So I'm not sure why yours doesn't fit because this guy knows his Sierra's.