Will depend on the markings which will give you a range of approximate year of manufacture.. The pony placement is the best start.
http://www.coolgunsite.com
Click the ID Pages then Markings.
Then buy yourself this book which will lead to buying more M1911/A1s...
From this single picture it looks like you did great at $400! More/closer pictures would help give me a better idea.
Do the stocks have the matching serial number written in pencil on the interior of the panels?