You may want to look at F/FGA too. One issue with FTA/FGA across eras is that free throw rules have changed:
-three to make two
-two to make one
-flagrants
-the bonus after X fouls in a quarter or x time left in a quarter/half, etc.
I'm not sure how the three to make two rule was recorded. If a player made the first, misssed the second, and made the third, was his stat line 2/2 or 2/3? I think it was 2/3, but I'm not sure.
If you want to go w/ the full F/estimated possessions by year, it may be easy to copy and paste the league average line from the team statistics table for every year from b-r (1961-62 is here):
http://www.basketball-reference.com/leagues/NBA_1962.htmlIf you're feeling really ambitious, you might want to control for usage patterns across positions in different eras. For example, FTA/FGA in the early 60s was higher than it is today or in the late 70s/early 80s. Intuitively, it doesn't make sense to me at least. I would expect a faster pace environment to be due to guys taking the first open shot they see. The first open shot would lead to a lower F/FGA...unless it led to a massive scrum under the basket due to lower FG% of the era. Or the higher foul rates could be due to the centers of the era. You could look at F/FGA or FTA/FGA of small forwards and guards only across years if the numbers look a little funny to see if this is the case.