SUPERCHARGING 400 SB

What do i need to do to supercharge a sb 400. it was rebuilt 6 years ago but has had less than 1000 miles on it since. i want to put a 142 or 144 charger on it but i really don't want to tear the engine down this year if i don't have to. i don't know the comp ratio but i believe its all stock. most of the cataloges claim their superchargers are pretty much bolt on but one speed shop said i need 8.5:1 ratio , new, bigger cam, forged pistons and 4 bolt mains...does this sound right or can i get away with the stock engine as is. i can see doing all that if i was going to a 6-71 or 8-71 charger but not a small street charger. paxton chargers claim to be bolt on and go so what's the difference................... ........need some guidance