No way to answer without the serial number. You can call Colt and they will tell you if you provide the serial number.
@1964
1974
Proofhouse.com has Colt sn data.
You must call Colt with the serial number to find out.
1970
value depends on overall condition
1000 USD
Impossible to answer without the serial number. Call Colt and they will tell you for free.
500-900 uSD
1977.
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