my bro put a 6 speed 350z gearbox in his s13 sr20, all he had to do was get an adaptor for the bellhousing made up, mod the gearbox crossmember, get a 350z tail shaft and get that modded, and just chop up and get the remote shifter moved foward cos the gearbox is pretty long, but it fits and has really low gear ratios so it acclerates f**ken quick! the gears are huge in these boxes we had it apart and the thickness of each gear was the biggest i have ever seen. So they should be strong enough. It was a good mod if you ask me