318 with 340x heads sluggish

Now you are killing the next guy that buys x heads to put on his 340. Now you need to address intake on how much you mill...

I used to build 70's 318's with 360 heads, they were cheap, and they always ran good. Always milled the heads, block side, .020 or .040, and intake side, .019 or .038...

If you are milling heads, this makes it a no brainer.