Holley,
It sounds like you have a nice rifle. Time will tell if it is a shooter.
Is this gun any good?
It is a Knight Rifle with a Green Mountain Barrel. I would guess it is a very good rifle.
Is there a 209 conversion?
From what I have read, one is offered through Knight. Like Underclocked said.
Good load to start with?
80 grains of powder and a 240 or 300 grain XTP. You could also try some 250 grain Shockwaves, or Knight Red Hots.
The barrel looks pretty grungy...would you use a brush and bore solvent?
I would take and clean the rifle top to bottom. I think you can down load a manual from the Knight Web sight that will tell you how. And if the barrel is ruff looking, by all means take a brass bore brush and some solvent and scrib that barrel out real good. If you have some J-B Bore Paste I would actually use that and really scrub the bore. After that if you're not going to shoot it, put a good coat of oil in the bore to protect it.