If you go all the way to the bottom of that page you will see a list of sketches. You are looking for the sketches labelled "Back (inside View)", "Back (Outside View)", and "Groundglass Frame".
Alter the interior dimensions to match your film holder and the outer dimensions to fit your camera. Use your 5x7 back for reference.
As long as you have the registraion distances correct, you should not have much problem, the design of a spring back is really one of the simplest forms of backs for cameras, you just need to make sure when designing that the GG sits in the same plane as the film in the film holder so that you get true focus..