Hi Peter,
I met a Stalwart owner at a military vehicle event in Australia, earlier this year. He has done extensive mods to his vehicle, including fitting a higher ratio gear train in the transfer box, giving him a road speed of around 60 mph. He has also fitted a declutch system to bevel boxes, forgot at present how he did that, but think it is only the leading axle that can be disconnected. He has a LPG conversion on it, and this is where you will want to know. On the long run up to Corowa from Melbourne, he was suffering icing when running on gas, and had removed the large fuel tank for a small one for starting up, so had to keep topping up the petrol tank and run on petrol more than he intended. Not sure if he is on this forum, but comes from Geelong in Victoria.
regards, Richard