I honestly would not worry about all the drama. Bolt the damn w2 heads on to the 318.
The car will still cruise and idle. Sound mean as hell.
The small rpm differences be damned and peak hp crap. When cruising the roads who will notice?
When wanting Crack the throttle boil the tires and scare the small women and children while you grin ear to ear in pure acceleration fear.
Tell everyone they got smoked by a 318. Who cares what everyone thinks or wants to tell you.
If they ask if the car is numbers matching you can say yes (because the ownership matches the car in your name)
The flip side. Around here 318s are more plentiful then the 360s. Blow the 318 up or window the block... go get another 318 at the wreckers and they will be cheaper because nobody wants a 318