Fire Jeep
While 1/25 is the most common scale for automotive modeling, as a 1/64 scale model railroader, I've 'prepared' lots of 1/64 scale vehicles for use on the layout.  Sometimes this involves just dulling down glossy finishes and adding light weathering but in other cases I've 'bashed' together whole vehicles.  Here are a couple of my favorites.
1932 Ford Gasoline Truck
This fire-fighting jeep was modeled from a photograph that appeared in a local newspaper in Widen, WV in the mid-1950s.  The caption announced the acquistion by the local coal mine of a piece of "Modern Firefighting Equipment"...a jeep with a couple of tanks for water, a large reel of hose and some kind of pumping mechanism.
The manufacturer of the 1/64 Jeep isn't known.  The hose reel and tanks were scratchbuilt.  The hose is wire.  Car modelers might recognize the silver 'pump' on the back as Weber side-draft carburetors from a 1/25 kit!  Pastel chalks were used to lightly weather the finished vehicle.
1941 'Dodge' 1-ton Truck
A friend, Cody Burdette, had a 1941 Dodge 1-ton flatbed truck that looked like this.  I built a model of it for my model railroad.
I could not find a 1/64 model of a '41 Dodge but decided that a '40 Ford was 'close enough'.  The cab was cut from a '40 Ford pickup, the chassis was made for styrene, the wheels and tires were from my scrap box and the bed was built from basswood strip wood.  The license plate was made on my computer.  The vehicle was lightly weathered with pastel chalk.
This free-lanced 1932 Ford gasoline truck started as a Matchbox panel truck.  The vehicle was cut off at the rear of the cab and a new frame was fabricated from styrene.  The tank is a plastic item from the scrap box, like the small fuel tank mounted behind the cab.  The source of the wheels and tires is lost to history.  The hose is a piece of wire.  .020" brass wire was used to make the grabs.  On the right is the
truck in service on my 
model railroad.