James, you are right and the W58 is going into my car coupled to a 3SGTE engine which I am now in the process of reconditioning. The reason I stuck with the W58 is the fact that it is plentiful in my country and it is rated to handle 230hp safely as stated in the box specifications of the link I provided you with. My engine std makes 225hp
The W58 is a firm favorite in SA for light truck conversions and replacement for the weaker Isuzu box
(and others) and also when bigger engines are installed in cars/trucks the W58 box is king.
Here is a link to my build diary and it will take you to the last page:
http://www.lotus7.co.nz/forum/viewto...=1530&start=60
The tunnel width is still std at the engine side but greatly reduced inside to get the sports seats fitted and still the W58 slips in with space to spare. There is a section in my diary of this change and the amount I removed.
As for what box to use, that is your decision alone my friend but to help you decide, here are two links where these boxes are discussed. I am not on speed on the J160 box....
http://www.toyotaownersclub.com/foru...p/t100976.html
http://my.is/forums/f114/altezza-j16...le-2jz-366061/