Manifold

I suppose you could port the intake out to match the ports on a 340/360 head, but I would think you would be better off getting an intake manifold made to fit you cylinder heads.

If you have 340/360 heads, then buy the correct intake. There are plenty of used ones around that at least as good as an LD340 (or LD4B). Even a new Mopar Perfomance or Edelbrock intake (which are supposed to be better than old intakes) will cost $250, how much time will it take to open up all eight of the intake runners. How hard will it be to try to make them flow the same amount? How much is your time worth? Can it spent doing other things on your project car?

You can probably find someone who needs the 318 intake to sell it to and offset some cost of buying a 340/360 intake. I have an LD4B and plan on using it on a 318 in my 67 cuda even though I own a few spare 340 engines, cause with gas at $3 a gallon a mildly modified 318 will be plenty fun to drive and way more economical than a 340 .

Bob