I found a Colt diamondback with that serial number made in 1971.
what is the manufacturing date fo a colt diamondback serial number O72239
Diamondback serial # D69679. was mfg'd in 1975. made about 1976
1969 value guesstimate around $450
On the frame
You will need to call Colt to find out.
400 to 600 dollars depending on condition and where you live.
On the bottom of the mono block.
1977
made about 1977
Around 1968.
if the diamondback model should be about 1974