The US Army made a similar vehicle called teh 1/4T Mule. it had 4 wheel steer, and an air-cooled engine in the rear. It isn't street-legal, however.
Here's the data for the Halflinger (translated with my fractured German):
Four cycle boxer (opposed cyl) motor, air cooled
# of cylinders: 2
Bore 3.149"/ Stroke 2.519"
Displacement 643 cc's (39.7 cu in)
Motor Power: 24 hp @ 4500 rpm
Torque: 4.2 mkp @ 3000 rpm
Compression Ratio: 7:1
Valve arrangement:
Camshaft: In crankcase, gear driven
Crankshaft: ????
Lubrication: Pressure system
Oil filter: full flow; micro filter media
Oil Cooler: flat tube
Oil Capacity: 2 liters (2.2 qts)
Cooling: Air Cooled w/ axial fan
Electrical System: 12 V battery and generator
Carburetor: Fallstrom downdraft
Fuel Pump: Mechanical diaphragm pump
Air Filter: Oil bath type
Engine location: At rear with transmission
Clutch: One dry plate
Manual Transmission: Indirect shift, 4 forward gears, 1 reverse gear, transfer case with 1.65: 1 ratio
Transmission mounting: with rear axle unit.
Axle System: 4 wheel drive by spiral cut gears and differential. Front axle driven by shaft from rear differential
Transmission ratios: 3.73/2.18/1.30/.71 forward; reverse 3.55:1
Axle ratio: 4.22 (9.38)
Tire ratio: Different possibilities: 3.0, 2.72, 2.38
Top Speed (@4500 rpm, depending on wheel ratio): 52 km/hr (31 mph);58 kph (36 mph); 64 kph (40 mph)
Steepest grade - 1st gear/dry soil. 65%
Maximum side grade: 45%
Differential lock: in both axle systems; hand shift on the fly.
Frame construction. Central tube system with both differential housings and transfer case; independent swing axles
Suspension: Front and rear coil springs with hollow rubber progressive springs and double acting hydraulic shock absorbers
Brake operation: Foot operated hydraulic brakes; special alloy brake drum with cast iron hub; welded backing plate. Hand brake actuates rear brakes.
Wheelbase: 1500mm (59")
wheel track 1130 mm (44.5") front & rear
Clearance 240mm (9.4") under axle housing in loaded condition
Ground clearance 300 mm (11.8")
Wading depth 500mm (19.7")
Turning circle 7meter (23')
Approach angle: 45% front; 40% rear
Greatest Length/Width: 2830mm/1350mm; 9.3 ft/4.43 ft
Greatest Height: 1740mm, 5.7 ft
Cargo area: ~2 sq meters (~2.2 sq yds)
Fuel tank Capacity: 30 liters, 9 gallons
Empty weight: ~ 600 kilograms, 1,320 lbs
payload: 500 kg, 1100 lbs
Max. wt: 2,420 lbs
Axle capacity: 1,100 lbs frt; 1,320 rear
Trailer wt:~ 660 lbs- no brakes
SmittyII