How to get 400 hp out of 1971 340 .30 over

Ive never sprayed this motor
i sprayed a 68 dart 270 318 340 heads hemi cam torker door stop 650 dp 3.23s
Also sprayed a70 duster 340 243@50 gk cam same torker door stop same 650 dp carb same unilte 3.23s
This motor came out of 68 gts i raced@80k miles ran 14.3@97 plus all stock 3.23s ended up being junked
That motor is in my 67 gt vert now
any more questions smart ***?
pardon my conflating the facts, what with all your posts being so easy to decipher.