I welded four 2x2 posts onto the original subframe about 2" high on each side then I ran 1x2x.125 tubing along the tops of the posts to give you the main side frames. I connected the two sides with 1x2 cross braces which are later cut for the driveshaft to go through once you get your tunnel loops welded in.
I then boxed the main pillers with some 1/8" steel and connected the subfloor to these. At the rear I used the main cross brace under the window and welded in another piece of 1x2. More cross braces were added as needed to give it a solid structure and something to weld the sheetmetal to.
The cowl was the hardest part to figure out so I kinda copied Dons idea by welding a steel plate to it and connecting everything to the plate. I closed off the front welding everything together to make it solid. It just kind of makes sense once you start doing it and you can see what you need to do.
To mount to the frame I just drilled holes into the subframe through the chassis frame and welded some large grade 8 bolts to the chassis frame.
I'll post the pictures I got, if you need more let me know.
Sean