[Nine-one-one]

Hi guys, would like to know your opinion on what gearbox to use on a 78 SC build.

Car is a 78 SC which im backdating at the moment and i will use the 3liter engine for now. Would like to keep the option to maybe switch to a 964/993 engine later so having some safety isnt wrong, but for now im using the SC's engine with a goal of around 240hp.
Whats the best gearbox for this car? I bought the car as a rolling chassis with just a engineblock and some spareparts, so dont have any gearboxstuff, which means im pretty free what i can use.....but would need to decide now, as the chassis is nearly paint ready. So if any modifications need to be made to fit a newer gearbox, now is the time.

A german company uses 997 GT3 gearboxes in their G-modell builds..... whats needed to do this? Could a 996 gearbox be used??? Reason i ask is these gearboxes can be bought pretty cheap and are surely way better engineered then the old gearboxes, so if its possible i would rather buy a new later gearbox then lets say a 915/G50 box that allready has been used for 25 years or more.

Very interested in the answers....
Best regards
Alex