Transmission tunnel type 9 or mt75?

[Shorty]

Hi, just planning ahead at the moment but hoping to start chassis soon and I am wondering if there is much difference between the two and is there any drawbacks of either?
I was planning on sticking with the type 9 as I wanted to keep to the book as much as possible for simplicity for my first build but did want to use a zetec rather than pinto as they are getting very scarce.
I understand that the mt75 is slightly bigger, so just wondering if it is best to make the chassis to accept the larger gearbox then you would have the option of fitting either box?