The first years of the SKS had spring loaded firing pins. it was mid 51 they switched to a non-spring loaded design.
I have the spring kit from Murrays and have had no FTF with russian, czech surplus or home-rolled. the spring pressure is minimal really. should measure it but... have you ever had your finger between the disconnect and the hammer when you are firing the trigger assy?
the only time i have had FTF is when i tried to lighten the hammer spring to get a lighter trigger... bad move.
that said, as boultonscouter stated, if you keep it clean (so it rattles up and down when you shake it) you are good to go.
get yourself some pressurized cleaner like crude cutter and don't be afraid to pull that thing apart (firing pin assy) for a cleaning.
cheers and enjoy your SKS!!!