Pivot angle measurement and marking of rear frame cut

I have a platform for painting ceilings.  The underside has strengthening steel angles.  I used this as a straight edge to clamp the front and rear frames in line and used some threaded rod through the pivot to set the steering angle of 63 degrees (with the invaluable help of Sarah, seen holding the protractor in the picture).  I used a magnet to fix the rear frame in the correct place and drew a line at the place where I needed to cut.  

You will notice that the rear frame is upside down in the photos.  Thankfully I noticed my mistake before cutting and went through the whole process again to make the correct cutting marks.