score! but i need help

Oh, on the 318, I would not waste the time and energy with it since it's just spending money on the true goal at hand.
It is truly not a case of if you can make 400 with the 318.
The only thing I would do to the current in car engine ( 318 ) would be header and full exhaust since theres no diff. in swaping in the 360 later. There will be no problems. It all bolts in perfectly.
Ignition. Again, can be carried over to the 360.
Everything else should be stored and assembled new, unused on the 360 for max impact in everyway. Including a max smile on your face.
Take it from me, the been there done that for 21 years of tinkering.
You'll thank me later.

Oh, also, I think your on track fine for 400+ HP at the flywheel.