It is a Trooper Mark III. The 8" barrel and rounded grips indicate that its a later production gun.
Go to this site: Colt Serial Number Lookup
and enter the full serial number to get the year of manufacture.
Value is hard for me to say. In General, Mark IIIs are less desirable than other Colt revolvers. Usually in the $600-800 range. I recently bought a 6" .357 Mark III for $625 which I thought was an excellent price.
However, prices on Colt revolvers have been sky rocketing recently and add that this is a scarce .22 with a 8" barrel makes it even more valuable.
I'm by no means a Colt expert. But if it were mine, I'd be thinking in the $1200-1500 range. I'm sure one of our resident Colt experts will be along soon with a better idea of value. It may well be worth much more.