S15 6 Speed gearbox I purhcased off ebay [$640 AU].
To my knowledge the 5 speed Silvia boxes are pretty easy to fit, just have to change the Silvia box's bellhousing to a Z's bell housing. The 6 speed is a little different:
The 6 speed is made of of 3 parts where the 5 speeds are made up of 2 (see pic). Because of this, the bellhousing from a Z box won't fit onto the S15 and the bolt holes from the Silvia's bellhousing don't line up with the Z engine.
Also, the 6 speed is 100mm longer (see pic) (therefore stick sits back another 100mm and doesn't line up with the standard hole, the gearbox mount is 100mm further back and the driveshaft will need to be shorter).
Based on a 1981-1983 280zx factory 5 speed taken from The Z Design Studio and S15 information take from 200sx.org
| Gear | S15 6 Spd | L28 5 Spd |
| 1 | 3.626 | 3.062 |
| 2 | 2.200 | 1.858 |
| 3 | 1.541 | 1.308 |
| 4 | 1.213 | 1 |
| 5 | 1.000 | 0.745 |
| 6 | 0.767 | - |
Our plan at the moment is to make an adapter plate to fit the Siliva bellhousing to the engine. We will extend the mounting bracket to fit and get a custom driveshaft made. The gearstick being 100mm back doesn't matter because I'm 6'4" and I have the seat right back anyway :S
We haven't had a close look at how we are going to do this. I will post more
info once we have made the rotisserie and begin fitting the gearbox.
This box was purchased through the trading post. It was listed as a 260z 5 Speed. The mounting bracket is a "saloon mounting bracket" and is "not one from a Zed". (Thanks to Tony D from zcar.com forums for the info)
This is the Auto box taken out of my 1977 260z:
