Any device used for hoisting or lifting needs a minimum safety factor of4 to one , 8 to one if it goes on my elevators. Any wire rope sheave needs a bend radius of 15 diameters 30 if it is used for hoisting.
For the occasional one time use you can get away with tighter bend radius one easy way to tell if a block will carry your load is to take the cross sectional area of the pin multiply by the yield strength divide by 4 to get safety factor
This is not the correct to do this but the down& dirty way. never assume the pin is any stronger than low grade mild steel consider that a 1/2" shaft pin with an area of .196sq" @ 36,000 psi yield would take 7068 Lbs to bend it @4>1 you would have 1767 safe working load And even at that it would be dodgy because no account was taken for the snap ring grove or the side plates or the looseness between the sheave & side plates the thickness of the side plates or anything else
even a 3/4" shaft pin using this way to figure only has .441" x36,000=15,894/4=3,976lbs. A well made snatch block will use 150,000PSI pin stock or better .441x150,000=66,150/4=16,537 and will only be rated by the MFG for 4 tons
when in doubt always try to err to the direction of safety