The LEE jeans arrived in the mail from my friend Linda, along with some extra denim and a 24 inch zipper. Linda tells me that the left leg of the jeans needs to be 23 inches around at a point 9 inches below the crotch, and 24 1/2 inches around at a point 13 1/2 inches from the crotch.
I added an inch all the way around this shape-. Go oversize- you may have to make it bigger, and then you will be glad you have the material to work with. Also, add a couple inches length to each end of the gusset, so you have some flexibility on where to begin and end the zipper. Now the sideseam gusset is a solid piece of denim, but the inseam gusset is made up of two strips of denim joined by a 24"zipper. My gussets had to add 7 inches to the leg- so each one had to be at least 3 1/2 inches plus two seam allowances, at it's widest. The two strips for the inseam gusset each had to be 2 inches plus two seam allowances. I made the strips 29 inches long.
Open the zipper to sew the halves of this gusset. I did this one first, Then, when you do the second gusset, you can leave the zipper open.
Here are both gussets, and the bottom hem has been redone, too.
More miscellaneous: I used a 3-step zigzag on most raw edges. I Used FrayCheck on raw edges that I could not reach to zigzag. This is denim, it is going to fray if you don't put up a positive defense. How I found matching denim: I took the pants with me to the thrift store. I found a pair of jeans that were the same weight and manufacturer and a nearly exact color match. One pair of thrift store jeans will gusset four pairs of jeans.