Thanks Vombil, Panoz, advice is well received. Digging deeper, I just worked out I've got a 4L60E version of the TH700 so things got a bit more complex. I'm leaning towards a 304 basic rebuild and transmission overhaul so it can slip it all into the 1 tonner as a daily driver. The reliability and fuel economy is very appealing and to be honest, i cant see the 1 tonner getting much benefit from a massively souped up drive train. Probably just spin wheels worse than is does now with the 308.

I will do one more check to make sure the engine hasn't already been stroked (unlikely) but a basic rebuild looks worthy. Worst case, I could strip it all and sell parts on eBay...