The gearbox dipstick fitted to the ie cars is completely different to that fitted to the earlier cars. It sits in a long tube so you can access it from the upper part of the engine compartment without delving under the battery tray etc. From memory the tube is narrower than the short early dipstick.
I'm guessing you have an ie box without the tube fitted?
I believe that the box I've fitted to my carb engine did come off an i.e. but when I bought it there was no dipstick fitted - something I never thought to check for at the time. I've had a word with Mark W and he reckons he can sort a suitable dipstick for me from his collection of spares, so all is not lost. The elongated dipstick and holder would make it easier to check levels, but I'll be happy if I can just find one that fits...