Just have to back track a bit here for clarification purposes
above in the laying out of the "L" shape I meant to say "the long leg is 2.5" wide (instead of thick), and the "short leg 6" wide (instead of thick")--you probably understand that the piece of material we are working with is already 4" thick
Sorry about that--trying my best
Now the tricky part--let us take a look at what we have now --we are looking at roughly an "L" shaped part with a long end 2.5" wide and 4" thick rounding into a short end 8" wide and 4" thick, we will be working with the short part and the underside surface
Now we should know where we are--it is on this surface we will be laying out and shaping a Dovetail the full length of its surface--this dovetail will be heavy in construction--roughly 1.5" on its flat surface and no less than 3\4" wide where it intercepts with the new surface--this means that a fair amount of ingenuity, work and skill will be taking place to create this important part, and there are 4 of them to create!!!
Now lets fast forward ahead a little--say we have them all done and now what--well on the outer surfaces of the WSG's eventually there will be dovetail mortises to accept the dovetails we are creating, I believe (hopefully) that you are starting to get the broader view of what we are creating, having said that, and if your work is of good quality the "L" shaped support's dovetails should slide snuggly into place and be ready for the next step
would anyone out there with sketch up or a similar sketching tool be prepared to venture a picture of what I am creating for everyone to see