I ran a Detroit in the rear of my 91 for 5 years. For the most part it worked great. But, if I got on a slippery off camber slope in the snow or mud it was game over.
My buddies stock 98 Tacoma with all terrains drove up a muddy dougway to our spring turkey camp and my cruiser with 35 mt's...
Keep the gray one and do what @Nemesis1207 said.
Harrrop in the back and keep the front open.
Goodluck and I look forward to seeing this thing get built and photos from the pan america trip.