[Van]

Well here's a basic structure in SketchUp. Quick notes on construction:
Two upright pipes should be secured to floor with standard flanges.

The Two horizontal pipe should be parallel.

The two scroll pipes should be standard 4" exhaust pipe. Weld several 1" square steel tube pieces about 3 Inches long inside the end of the exhast pipe, this will allow you to weld a 3/4" scd#40 pipe in the center of the exhaust pipe. < 3/4 scd #40 has an exterior diameter of .95" which is awful darn close to 1".

The 1" pipes should be held in place with Pillow blocks, mounted on 3"x2"x1/4" steel plates. the plates will be held to the horizontal pipes with two u-bolts.

the mobile nature of the mounting plates will allow you to "align" the scroll pipes getting them to perfectly parallel is a pain but absolutely necessary, just like on a belt sander.

you can rotate the drop by a crank attached to one of the 1" pipes or by securing a cog to the 1"pipe and then attaching a gear motor . Hope this helps. It's real quick and dirty, and I'll answer all the questions that are bound to come of it.

Ok I lied, I can't zip the sketchup file to less than 2 Mb which is too big to upload here. I attached a jpg of the drawing, I'll try to translate this into Autocad or see if I can reduce the drawing. < the cheeseboroughs are'nt mine and they are 2Mb all be themselves.