body drop w/ stock hood?

im recently starting a project, its a 1991 Nissan automatic and its going its body dropped 3 3/4" and will lay out on 20's i was just wondering what is needed for it to lay out on 20's (ex. aftermarket upper or lower control arms or modify the stock ones?) i know i will have to tub the firewall and i would like to keep the stock hood and i havent took any measure ments yet but i would like to know how far the motor will need to be dropped and whats involved, especially because its automatic the tranny pan hangs down and just need some one elses opinion about what i should do ? if any one can help it would be great?