The Obama administration has approved the first American factory in Cuba in more than half a century, allowing a two-man company from Alabama to build a plant assembling as many as 1,000 small tractors a year for sale to private farmers in Cuba. The Treasury Department last week notified the company, owned by Horace Clemmons and Saul Berenthal, that they could legally build tractors and other heavy equipment in a special economic zone started by the Cuban government to attract foreign investment. Cuban officials have endorsed the project. The company said it expected to begin building tractors in Cuba by the first quarter of 2017. The plan, expected to cost $5 million to $10 million, would be the first significant United States business investment on Cuban soil since took power in 1959.