NP205 is far superior to the NP203. Course the new Atlas 4 speed is even better, but big $'s.
The 302 will give you that cool nostalgia engine. Lots of torque, but no high revs, and parts are expensive. You can install a 454 in that engine bay, with some "enlarging" of the firewall and "modifications" to headers. I don't know if a tall deck 427 will fit. SBC will fit no problem.
400 tranny is better than 350. How much torque you gonna put through it?