You can't just bolt on Horse power. I'm building my engine from the ground up. I've got a 348 engine that I am going to stroke and bore for between 434-440 cid. Going to make it look like a 409 engine. You really just can't replace displacement unless you start going into forced induction.
You could do something similar with your car, but even though mid production a 409 became available I would make it look like the 350 HP 348 with triple deuces.
W engine performance builds though are not for the faint of heart. Number estimates keep climbing a little and by the time the engine is in the car and running I'll have close to 10 Grand in it. All the little things you forget when doing something like this adds up. New larger exhaust, accessory brackets, fan shroud, and more all cost money when they have 409 in their description.
Sorry ... I was referring to the rear differential. How to upgrade the rear differential to TRANSFER the higher HP to the wheels, not produce it.
The dressed blueprint engine which has my eye is the 383 stroker which is rated at 425HP/430 ft/lbs. I thought that was quite a lot!
... I don't want to spin the rear-end out of it, but I've had it perform with the 283 quite well (smoked the tires from a down shift 3 to 2 at 40ish mph back when it had a manual)
LOL ... yeah, no replacement for displacement.