If you were running 340 or 360 heads, you had the big ports already. Isnt the LD4B the 340 intake? It would have those ports anyway. In terms of back to back testing, I havent done it. But as I recall, a few guys did, and the RPM and RPM air gap (same basic designs) were tops for dual plane intakes. The LD4B was very good for it's day, and still a good choice for sneaky stock-type looking intakes, but the RPM will beat it all across the board.
