I have the same exhaust kit you have, and I have the mufflers mounted in front of the axle. I've never considered it too loud, but I guess that is up to the individual. So I downloaded a db meter app for my samsung s4 and tried it out in my car. I got 79 to 80 db when idling in the garage. I don't know how accurate the app is?
But if it is anywhere close to accurate, you must have another issue other than the exhaust system kit. Maybe the old rusty headers contribute to the problem? Does the 'X' pipe get close to the driveshaft? Headers rubbing on the torsion bars?