Best of luck to ya, you're going to need a ridiculous cam (high lift, probably higher rpm), higher compression (38cc TFS will do this, but you'll still probably need some more from a new set of pistons) and possibly a better intake manifold to flow the kind of air you'll need.
Remember, this engine is only 281 cubic inches, and that means your 400hp will be way the hell at the top of the RPM range and you probably won't get past 360 rwtq.
The build will be all sorts of big amounts of money that might make you reconsider your options. After all is said and done, you will have put in probably a little more than it would take to throw a centri on it and call it a day with over 400 easily. It will probably be the single most frustrating build ever, because after all is said and done, you will:
a) come close to your goal, but not there, or
b) have the most unpleasant driving car in the world- it will drink gas, be loud, and you won't be able to cruise at any rpm below 1500 without the car bucking wildly.
These are just the things that go with having a small, naturally aspirated engine that has been pushed as far as it can go without FI. It's your choice, yeah, go ahead, do it- but as I said before, I haven't seen it done. Best of luck to you, good sir, and Godspeed.
