Ok, so.....
I've now got over my initial excitement around unimog's and big ex army trucks, and am back to the rational world of timber lorries. There are too many grey areas around hauling with a Mog, and realistically it will end up being way more expensive, even if Mogs are cool and would be better on the slippery stuff. I'll just have to treat myself to a u406 for fun once my timber haulage firm as made my fortune!!!
That big Foden is not going to be practical, as much as I am a fan of big MOD trucks, having looked on the Military forums they seem to go wrong far too often, and spares/maintenance is likely to be a nightmare.
So, it's (almost) definitely going to be an ex-brick lorry with bolsters and a headboard added, and the brick grab swapped with a log grab with weighing sensor! Get a proper O licence and HGV/Hiab ticket and will be ready to go, and provided I can sort out all the necessary funding I hope I'll be up and running next winter.
Currently getting quotes from engineering firms for the conversion, and then going to put in for an FC grant, even if they will only part-fund the bits for the conversion it will be a start!
Thanks for all your help and advice. Wish me luck