AS far as i know there are no templates for the Jango holsters, i have looked for them myself. I would say looking at the pictures though, the straps are actually sewn into the base of the holster. I would also take into consideration the different grades of leather. The base i would say is thicker than the straps and the face of the holster.
One thing to consider though, is the Jaster in the comics and the 3 3/4"figure doesn't have Jango holsters.