You will have to call Colt with the sn to find out.
Looks like a 1975 SP1. Here's a link to Colt Ser# http://www.biggerhammer.net/ar15/ar15serial.html Good luck 7.62
@1964
Colt first introduced the AR-15 SP1 in 1964. This model was the civilian version of the military M16 rifle and marked the beginning of Colt's production of the AR-15 platform. The SP1 became popular for its lightweight design and modularity, setting the stage for the AR-15's evolution over the following decades.
1974
100-1500 usd
Proofhouse.com has Colt sn data.
value depends on overall condition
1000 USD
1970
You must call Colt with the serial number to find out.
The Colt AR-15 Model SP1 with the serial number SP 204803 was manufactured in approximately 1979. Colt typically produced the SP1 models in the late 1970s and early 1980s. For precise dating, you may refer to Colt's manufacturing records or consult a Colt historian.
Post 78 given the sn you provided