Happy New Year,
This post is a bit confusing because I have not read the other web site. The side of importance for this would be the vertical sides, the 8 inch for 8X20, these would have the tapers at the ends.
It is easy to figure out if you draw it out full size. You need to find the Max. & min. sizes for the rear body and front standard. Also the Max. length and min. compressed/ closed length. You need all the specs. to figure the growth rate per pair of folds and how many folds will close into your camera body.
On 8X10 and larger the folds are usually 1 inch but you may need to make them smaller at the very rear so it does not vignette the film.
For building bellows you will need normal tools PLUS 2 special tools:
a 1/8 inch punch
a 3 bladed knife
You will need to make the knife yourself.
Good Luck With it.