When you model a vehicle first thing you have to do is to match it's dimensions either by scaling blueprints (good blueprints) or adjusting camera matching if you want to create accurate model. There are some other ways but those two are the most common. Never model a vehicle using reference images set up the same way as orthographic projection blueprints, this will get you all sorts of problems, it may work on some simple shaped object. Here are dimensions for Willy Jeep Truck
Body Length: 183 3/4” (4,67 m.)
Body Width: 73 7/8“ (185,4 cm.)
Height: (overall): 74 3/8” (189,0 cm.)
Wheelbase: 118” (299,72 cm.) (this is what you ask)
Adjust your model to these dimension.