No as the cosworth 4x4 mt75 has a thicker main shaft i am told so will be slightly stronger,

Also if you change the front and rear diff to 3.9 ratio then nothing has to be done to the standard cosworth gearbox, you only need the drop gears if you leave the front diff as a 3.6 and change the rear to a 3.9 to make up the difference in rotational speeds

Thanks
Marc