In good condition it is worth between $45-$85. More if it is in excellent condition.
The model 303 came in .177 & .22 Cal production started in 1969 and discontinued in 1993. Unfortunately you did not state the condition of the rifle so no estimate of value can be given. Is it Excellent, Very Good, Good, Fair or Poor?
hooded stirrups are stirrups with extra leather over the front of the stirrup where your toe is to protect your boot.
No
Aligning front/rear sights
No
Aiming.
Aligning front/rear sights
Aiming.
Sight alignment is the process of properly lining up the eye with the rear and front sights on open or aperture sights.:)
Most aftermarket sights are fiberoptic types such as Williams FireSights or the Tru-Glo sights. I dont know of any specific target applications.
Best left to a gunsmith
the process of lining up a firearm's rear and front sights