Can someone advise the sewn in un-stretched correct length from sew point to sew point of the Elastic Strap that is sewn to the shoulder harness seat belt on a 1970 Mach 1 mustang. All my used ones have the elastic stretch completely gone so I do not know what that length is. Also it would be good to know if the original elastic straps where 3/8" or 1/2" wide.