Just bought one tonight without knowing much. A little research after I got home told me it was designed to be compatible with the old Holley 3 barrels, but it'll work fine with a 4 bbl. Anyone know the difference between the X and non-X? Anyone here ever run one? I bought it because it has the hole for the oil filler tube, and it was right there when I first looked at CL, like it was meant to be. Only $80, too. I decided I needed a manifold because I had removed the 4160 from the 283 in my T bucket, and I realized the manifold that was on there was an old spreadbore Streetmaster with some kind of four hole adapter with these angled holes for the primaries. I'll freely admit I don't really know what it is I was looking at, but it seemed sort of cobbled up (like most of the rest of the car), so I figured I'd just get a dual plane manifold meant for a squarebore. So will this be an improvement, or should I have just stuck with the Streetmaster? Is the adapter on there appropriate?