I'm not sure if this helps much, but here's the entry on Otto cars written by Brian Laban in The World Guide to Automobiles:
The Société Générale des Voitures Automobiles Otto of Paris was the first company to import Otto engines to France, originally as stationary units. The first Otto free-piston engine was designed by self-taught inventor Nikolaus August Otto, from Cologne, based on Lenoir's earlier work, and the Otto engine was in production in a factory at Deutz, across the Rhine from Cologne, by 1872.
In 1875, under the direction of Gottlieb Daimler and Wilhelm Maybach, Otto's annual production exceeded 600 units. By 1876 Otto had turned to making a true four-stroke engine, although he ultimately failed to gain a patent on the principle, and by 1878 the engine had become a great commercial success.
By the time the Société Générale des Voitures Automobiles Otto introduced its first cars at the Paris Show in August 1900, it had been building Otto engines under licence for over 20 years. Two models were shown, with front-mounted 7 and 12hp vertical twin engines (although another contemporary report lists them as 6 and 10hp models, respectively of horizontal and vertical type). The company announced that it did not intend only to build Otto-engined models but also planned to use the Diesel motor, for which it had secured the French manufacturing rights.
By February 1901 the company had moved from the Rue de la Convention to the Rue Lacourbe and in that month showed four cars in Paris, two horizontal twin-cylinder engine 10hp models and two vertical four-cylinder 20hp models, with steel reinforced wood frames. Electric ignition was standard, but with an Otto magnetic device as an option.
At the end of 1902 the company offered a much modified vertical single-cylinder 10hp model with engine speed regulated by a variable exhaust valve. This gave much more flexibility than was then common, with engine speeds from 250 to 2000rpm claimed.
In 1909, after several years of building models broadly similar to the earliest types, Otto introduced a model called the FL, phonetically after the French pronunciation of Eiffel, the engineer and his famous tower. The FL was a fairly ordinary four-cylinder 12/ 16hp model which was joined by a six-cylinder 18/24 in 1912 but few were made because of World War I and Otto stopped car production in 1914.
There's a similar, but briefer, entry on Otto by Nick Georgano in his Complete Encyclopaedia of Motorcars. There are photos of Ottos in both books, but none of the FL model.