1973 340, want more power.
No, you can get well over 450 HP without stroking. Head flow and camming up properly are the keys, with other breathing improvements; intake, carb, headers and exhaust. It has been done a million times before so that number is very doable.
How are you going to be using the car/engine? Drag strip only? Street/strip and not a daily driver? Cruiser and daily driver only?
Be careful in chasing an HP number; you can get there several ways, but the torque curve that goes with a certain approach to 450 HP may not fit what you normally want to do with the car.