http://bamaroadster.blogspot.com/201...design_15.html
Have a look at mine. Its simple to make and works well and hard to get wrong.
I have amended it slightly since the drawings but the only change was to add a couple of angles on the front inside to allow it to sit on the table. And i cut out where the front frame welds are to allow the jig to sit flush on the bottom steel.
Any questions just ask
Andy