You will have to call Colt and provide the serial number to find out.
100-1500 depending on specifics
Proofhouse.com has Colt sn data.
Colt data at Proofhouse.com
You will have to call Colt with the sn to find out.
Colt has not offered a AR15 in 308
Looks like a 1975 SP1. Here's a link to Colt Ser# http://www.biggerhammer.net/ar15/ar15serial.html Good luck 7.62
Anywhere from 300-1500 USD depending on EXACTLY what you have, condition, accessories, manual, box, etc..
You must call Colt to find out.
You will need to call Colt.
If it is one of the recent Colt .22LR AR15 rifles, then the answer is no - they are completely different internally.
No such model in the Colt line.
Proofhouse.com has Colt sn tables. You can also call Colt and they will tell you.