Strip the Austin 12/4 back to its specification sheet and the character is already there: 1535 cc Straight-4, 24 bhp @2,400 rpm. British Motor Corporation built from 1933 to 1939, when streamlining and independent suspension were arriving together.
The background
The Austin Light Twelve-Four is a car that was produced by Austin from 1933 until 1939. It was replaced in 1939 by a completely new car also called the Austin 12 which kept the same engine. The "12" in the name referred to the taxation horsepower, a British rating which controlled the annual taxation payable to use the car on the road.
The engineering
Power comes from 1535 cc Straight-4; 24 bhp @2,400 rpm is the published figure. It shifts through a in one unit with the engine: single-plate clutch, 4-speed centrally controlled gearbox with synchromesh on 2, 3 & top.Three quarter floating rear axle. The wheelbase is 106 in / track 4' 2", 50 in. These are manufacturer figures carried by Wikipedia and Wikidata, not road-test measurements.
Where it sits
Its family tree is legible: it took over from the Austin 12 hp ("Heavy" 12); its successor was the Austin 12 (1939 model); assembly was at Longbridge Plant. Its contemporaries in the catalogue — the Vauxhall Cadet — show what else the money bought that year. Its British Motor Corporation stablemates include the Austin 10 and the Austin 12.
What it costs now
There is no federal ownership record for the Austin 12/4 — it predates the complaint database or was never sold in the United States — so MotorJury publishes no running-cost figure for it. For a car of this age the price is set by the collector market and the condition of the individual example, not by a formula.