I like a good challenge. I like a challenge that is achievable, anyway.
In 1947 Hamilton introduced a new movement to replace the 987A. The 6/0 sized 987A was the last of the series that started in 1927 with the 987, proceeding to the 987F and 987E. The movement that replaced the 987A was the slightly smaller 8/0 sized 747 movement.
In 1948 Hamilton introduced the Neil. It would continue to be produced for five years. So if you come across a Neil it could be from as late as 1952.