John, the box was made for me by Jonathan Panitz in Annapolis for around $150. It's made of Kevlar. I'll hunt down his contact info if that interests you.

What we *should* have done, in hindsight, is put the holes in the lid (removed in the pic), attach that to the carbs, and then turn the box on its side and attach it to the lid. That would make it a lot easier to get the horns on and off.

The intake tube is 3" PVC sewer pipe (should be smooth inside, whatever you use), and exits forward of the radiator bulkhead into the biggest K&N cone filter I could make fit. Crude but effective. I JB Welded a stub of the same pipe into the box, and the upper 90-degree elbow just slips over that, so it can move slightly as the engine moves.

The air horns are handmade by Unitek in Sweden. I don't think much of the Weber factory horns (swapping the new ones on put me back at square one on the jetting -- aaaarrrgh -- but that's an indication of how much better they flow), and TWM doesn't offer any for 48s that are long enough for our particular concept.

Steer clear of the sock filters, as they don't filter the big vent hole above the horns. That's actually an air intake for the emulsion tubes, not just a vent. Air entering there goes into the motor as part of the intake charge.