440roadrunner

Here's some things your really should think about.

You say this is "all original" does this mean that it's probably a "matching numbers" car?

If so, you really should think carefully about what you are doing.

(I know, we all tore these up, but that was back when they were "just cars." During the gas crunch of the early '70's they weren't worth much.)

all that has changed. These are collectible, and it won't be long before they are bonafide antiques. More and more of them that "are original" are just gone, so .....

consider this

If you want to build a hotrod, maybe buy a different car to build.

Or, pull the original engine and trans, document carefully every part, and swap in something like a built 360 engine/trans combo. These are plentiful, fairly cheap, and can be good performers, and much easier to find than 340s

Consider--you seem to have an original car. What happens if you happen to toss something through that origninal block? There goes the originality. In light of the overall potential future worth of your car, this could cost you tens of thousands of dollars.

Also, a true 400hp 318 is going to be very expensive to build, and when you get done you'll have a nasty thing to handle on the street. A 400hp 360 will still have a nice "cam" but be much more streetable, not to mention having a much better torque curve.