Seen one of these in an old catalogue; wasn't sure they actually existed. https://www.ebay.com/itm/Offenhause...y-/153078159156?&_trksid=p2056016.m2518.l4276
Here's another one on eBay now. Never saw this style before: https://www.ebay.com/p/Buick-401-425-Nailhead-2x4-Dual-quad-Intake-Manifold-Set-up-EELCO-EB24-59-66/761430947?iid=263779819575&_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=52910&meid=e984aec75d884319b6c87ec548b2dfdc&pid=100005&rk=3&rkt=4&sd=153078159156&itm=263779819575&_trksid=p2047675.c100005.m1851
Eelco makes good stuff. Marty was going to make an Aluminum single-quad manifold for the Nailhead, but I don't think it ever happened. JMHO, but I think that a pair of Quadrajets would be a bit much for anything but the most extreme Nailhead. The manifold would look great on a garage wall tho'...
Looks like a improvement over the factory duel quad as even those have a hard time keeping up with a well ported nail head. Line of sight looks much better at least viewing it from the outside!
Russ Martin offers a service to fix the flow problem with these intakes. ... does some milling from the top and accesses the internals by boring some holes in the bottom. http://centervilleautorepair.com/tech-info/offy-intakes
At one point in my younger days we put a factory nailhead dual quad intake with spread bore adapter plates on my stock 64 Riviera and it idled great And pulled hard. I am sure I never came close to using it to its full potential but it sure looked awesome. Cliff