But that depends on what heads your using, pistons, cam, etc. Or you have the option of buying a turn key crate motor for any amount of HP you want. Just be ready to empty your pockets.

 

A well built LS1 with good programing will get you close and will give "decent" milage. A high(er) nickel 4bolt block that is machined to accept a 400 rotating assembly(forged preferred) along with a good intake, high comp. pistons (forged preferred), a cam that gives good duration, lift, etc. (but will most likely idle poorly), aluminum heads that are built well will get you the power you are looking for....but probobly not the milage. I'll leave the rest alone as its been said before.