This awesome Dredge mod is courtesy of W. Wyatt of the WP forums
Changing a 4" Proline dredge to a over/under.This is an idea passed to me by Reek Lukins, a 5th generation gold miner from California.

one piece of miners moss 16" X 32"
one sheet of Aluminum 16" X 36" (the sheet we used was .065" thick)
one piece expanded metal 16" X 32"(We used 1" expanded but 3/4" will also work.)
one piece of aluminum angle iron 1" X 66"
Two shoulder bolts 1/4" with nuts
Two 1/4-20 round head screws

Step #1
Remove Riffle section and moss


Step #2

Fit aluminum sheet to the box leave 1" past stud for wave classifier,and drill a 5/16" hole where the stud that holds the wave classifyer down is.

I cut the piece to the width of the box.Pushed down on the sheet to mark the center and drilled the hole.

Step # 3

(Optional) Cut sheet so it will set flush with the punch plate on the wave classifier

Note see step # 11
Step # 4
Cut expanded metal to fit the bottom of the box.And place over miners moss
Step # 5
Cut aluminum angle iron into 32" lengths and place over expanded metal.
Step # 6
Replace wave classifyer
Step # 7
Replace the aluminum sheet.
Step # 8 ( optional)

Cut aluminum sheet 1" from bottom of punch plate and 1.5" from side to side of the center stud.

( explaination )I've found that some areas of the country have different types of "heavys" in the material you will be working.(Example) Lead shot,Magnitite,Helamite,copper,iron and black sands.I usually let my dredge run for awhile before I check the box for color to let the water work off the black sands and heavy materials.Now I've found anywhere from 4 1/2 lbs of lead to only one or two pices of lead shot in the box in Indiana. Many lbs of helamite under the punch plate in Colorado to just a few.So I made a modification to the plans Reed had made by cutting the drop area opening larger.
Step # 9
Cut the riffle section swivle/pivot point.Cut a slot the width of the shoulder bolt, So it can be removed for cleanup.

I used a jigsaw and cut it a bit wider that the original hole.
Step # 10
Fitting the riffle section.Put down the miners moss (and black ribbed matting (Optional)it depends on the height)Set the riffle section down over the moss so that the is held down tight and will not move. You may want to add matting to take up the extra space,or grind the sides of the wave classifyer down until it is tight.

The object to the left is the rubber mat or mudflap that is on the header box to flatten out the material over the punch plate.

Step # 11
Clamping.I think Reed used a bunjee cord to hold down the riffle section down his over/under wich is just as good as using the way we used by cutting the sheet in step # 3 you can hook a bunjee to the riffle section hold down and run it under to the other side.

Heres another pic of the clearance on the under box.