My proposal is change the current mid-engine and rear-engine gearbox to this one (from a Ferrari Testarrossa):
imgur.com/QsM1C3U
The engine is over the gearbox, and this maximizes the max capacity of the engine to be fitted.
imgur.com/00FDFhQ
imgur.com/QsM1C3U
It can be an option menu to select this format or the current one.
And the mid engined cars doesn’t use a big-sized gearbox. The Audbi r8, for example, uses a compact gearbox:
http://images.caricos.com/a/audi/2013_audi_r8/images/1920x1080/2013_audi_r8_29_1920x1080.jpg