Absolute longest gearbox!

[welshpug]

ypu wont want a box from the larger vehicles as they have bigger wheels and therefore lower final drives, something like a 205 fd with different gearing may be the way to go.

I don't think going really long will work however, you need to make sure its still in its efficiency range, there's no point making 5th so long that its cruising along under its boost area and labouring all the time.