Tom,
The earlier Arana papers I have seen are dated 1946. They are generally notes on greenkeeping and green construction. However, the Spanish Civil War broke out in 1936 and lasted until 1939, so I do not believe that Arana must have collaborated with Simpson at least until the early 40s
I believe Arana must have started collaborating with Simpson post 1940. The Spanish Civil War took place between 1936-1939 and golf ceased to be played in that time. After the war, Arana was "Golf Course Delegate" for the Spanish Golf Federation, where he was responsible for overseeing the reconstruction of existing golf courses - nothing could be changed without his approval. He resigned from this post around 1950 to avoid conflicts of interest with his remunerated design work.
His first design of which I have seen written evidence is remodelling work in the Pedralbes golf course in Barcelona (change of some holes and conversion of sand to green bunkers) in 1946-47. In 1948 he laid the first 9 holes of the Puigcerda golf course (holiday resort in the Pyrenees) which was later enlarged to 12 and subsequently to 18 holes.
Starting in the mid 1950s is when golf started taking off in Spain and between 1955 and 1968 he build most of his courses (El Prat, Neguri, Club de Campo, Guadalmina, Manises, Rio Real, RACE, El Saler, Ulzama, Aloha). Although the number of courses does not seem very high, at one point in time (1970) probably 30% of the existing layouts in Spain had been built or remodelled by Arana.
He probably learnt public relations from Simpson, as he disliked interference in his design work and would not accept jobs in which he did not have freedom to design as he pleased. He never returned to El Saler as one fairway bunker was removed in the sixth hole (it was restored in the 80s). In the 60s, with Spain's tourist boom, he turned down many projects due to real estate being prioritized over the golf course design.
His courses were long (he was a very strong hitter and liked to slam the ball) by those days' standards, always had a par 3 seventeenth (he was a match-play man) and always left one or two holes with a tree in the middle of the fairway (in one of the letters I have seen he tells the Chairman that he needn't worry about the trees in the middle of the fairways. They will surely be torn down due to members' pressure in the future...).
As a golfer, Arana had a very successful amateur career; he won the French amateur in 1934 and was finalist in 1935. He also won the Belgian, and German amateurs. Oddly, he only tried to qualify for the British Open once (1933) and never entered into the Amateur. In Spain, he won the Amateur (Copa Nacional Puerta de Hierro) in five occasions (1928,1929, 1930,1934,1939). He was also an accomplished sailor, having competed in the 1926 Olympics representing Spain.
I am writing a piece on Arana, so I'll hopefully I'll have something more ellaborated soon.
Regards,