1. Just tap the rear sight at the dovetail (notch). I use a wood dowell and a rawhide hammer, but any light hammer will do. Don't clobber it, just a firm tap is all you need. It shouldn't bend. The entire sight and elevator should move. Try just a bit of movement then test. Move the rear sight in the direction you want the group to go.
2. Just about most of the standard velociy .22 ammo will be around 1400 FPS. The CCI Velocitors should do fine. My Model 60's do well with CCI Standard Velocity, American Eagle's, Winchester Wildcats and Federal Lightnings. They can be finicky. Some Mod 60's don't like the Remington bulk pack ammo from Wal Mart, but the Federal bulk ammo seems to do well. I don't shoot Stinger or Yellow Jackets out of mine.
1. A bit to add:
Depending on the rear sight, there may be a small screw in the rear sight that puts added pressure on the dove-tail to keep it from sliding around. You may have to loosen this screw in order to adjust for windage. In fact, loosening this screw may make adjustments easy (no hammer/punch needed). If you need a punch, a brass drift won't damage the rear sight--use light raps, don't beat the heck out of it.
2. Standard velocity is around 1,200fps....
~1,400fps is not standard, it is high velocity.
Stingers are considered hypers, as are Aguila SuperMax's.
High velocity is recommended because not all subs and standards will cycle the action 100% of the time...My 60 seems to work great with standards, but not so great with subs.
Hyper's can be rough on the buffer in the action. I wouldn't recommend shooting them a lot, but a few rounds here and there should not pose an issue. I've put about 100rnds of Aguila Super Maximums (chornoed at 1,790 fps from my 60) in a row with no noticeable adverse affects. If you plan to shoot them a lot, keep a close eye on the condition of your buffer so you dont damage your reciever.
And lastly, a scope will not make the rifle more accurate--only aid the shooter in shooting more accurately.
I have a Glenfield model 60 (same as marlin) that will shoot under 1" at 50yds all day long with cheap off-the-shelf ammo at best with iron sights. My marlin model 60 with a 4x scope will shoot 5 shot groups under 3/4" consistantly with Wolf MT's...with the occasional group goin under .400 (luck).