If you need to replace a non functioning safety, these are generally not "drop in" parts, but require fitting by an experienced gun smith. If you are asking how to place the safety in the "safe" position, the thumb safety is pushed up to SAFE, down to FIRE.
'ACP' means Automatic Colt Pistol. A 1911, for example, would chamber a .45 ACP cartridge.
45 ACP
Any manual for a Colt 1911 will do.
You will need a gunsmith to find out.
about 250 give or take
The majority of 1911 models fire the .45 cal ACP. HOWEVER, there are several 1911 variations available, ones that shoot: .22LR, .32, .380 ACP, 9mm, 10mm, 40 S&W and others. On the weapon (typically on the barrel), the metal is stamped with the correct caliber to be used with that particular weapon.
1970
100-500 USD depending on specifcs
45 ACP
about 1913 value depends on condition
about 1978
Impossible to answer without hands on examination.