I know that since we almost only have fossilized teeth of this species, this is a hard task to determine the actual sizes of the jaws set in C. megalodon. But several reconstructions have been built, some seemingly with a rigorous approach and supervised by sharks specialists or paleontologists. Some of these, based on the largest and widest teeth, approach 2,50-3 m in TL width or height.

My question is : even theoretically, is it possible to use educated guess to estimate the jaws of C. megalodon, and if so, how large would be possibly the jaws in the largest specimens with teeth exceeding 5.5 inches wide and 7 inches long ?

Scaling organisms from individual body parts can be tricky and often only one or two body parts are used e.g. femur in mammals. The subject of trying to estimate the size of parts of the body, rather than total length or body mass is even trickier.

I found an edited volume on Google Books that has some valuable insight into the reconstruction of extinct Carcharadon species from C. carcharias but no obvious mention of jaw lengths

Great White Sharks: The Biology of Carcharodon carcharias
edited by A. Peter Klimley, David G. Ainley

"Hope is a duty from which palaeontologists are exempt."
David Quammen