There should be a set of letters and numbers stamped into the seat tube near the top; two letters followed by 6 digits, such as NC123456. The letters indicate where the frame was made frame. The first number should indicate the year it was made.

More information can be found on the following web sites:

http://www.sheldonbrown.com/retroraleighs/

If you check out the 1976 catalog page found on the link below, you'll see that year's model. Compare the decals shown to those on your bike. 1976 was the last year the Grand Prix came with cottered cranks, such as your bike has. Cotterless cranks were introduced in 1977. Based on this, your bike was made prior to 1977.

http://www.sheldonbrown.com/retroral...rand-prix.html

This following page deals with the various manufacturing date codes. Some what confusing.

http://www.sheldonbrown.com/retroraleighs/dating.html

Another site for Raleigh serial numbers:

http://www.jaysmarine.com/TH_raleigh_serials.html

Have fun researching your bike's history.