Why would you want to change it? The B60 has the same characteristics as a diesel engine plus it looks to be an early MK1 Ferret with early wings and two rear aerial mounts. Canadian or Australian maybe? If you change the engine and modify the rear engine decks, transmission and lengthen the vehicle you will only devalue the vehicle.
Jordan was the last country to modify Ferrets by adding a diesel engine they had to modify the vehicle with the modifications as above. If you think fuel is expensive in the US then you have to realise that it costs £1.39 a litre here and most of that is tax!!
Good luck with the Ferret it looks to be a good one :-D
Its you're vehicle so really its up to you what you do