Bruce,
HERE is a pdf version of the Northwestern car that was a tad smaller than the A5 yet had a Model-B engine that produced 50 horsepower. If you note, their claim was that this car would haul 200 men on trailers or 6,000 pounds.
It is also worth noting these cars were capable of speeds around 30 mph. Can you imagine riding on one of these without hardly anything to hang on to at 30 mph!!
.
.
.