The Tonner just looks like a sedan cut with the rear wall of a Tonner added. All would simply bolt down on a Tonner chassis no problem. Would cause little complaint from an engineer or rego office. Not sure why they wouldn't have used the Tonner tags though?

As for the TREMAC 6 speed to 308 sure it can be done but your transmission tunnel will need to change. These boxes are big, a lot bigger than the Aussie 4 slot. That said, they are a great gearbox once you fit a short shift to them. Speak to Dellow (Sydney) or Castlemaine Rod Shop (Vic) on the conversion kit. I doubt you would regret it from a strength or drivability point of view. Cutting up the car though might be a concern for some.