Im running MBRP resonators on my car with FI, cams, offroad h and borla S types....tone is amazing. Deep and throaty, all the rasp is gone. They are 12 inches I think. I originally had Pypes m80s but they started rattling so they had to go.
Off road H.... so no cats. Where did you have the M80's placed at the time... b4 the H, or after the H ? A local buddy had cherry bombs on the end of his LT, on his 1970 mopar..and burnt them to a crisp. They use aluminized steel alloy..which is junk, imo. Red paint all came off 1st, then the insides were burnt.
My setup is JBA ceramic LT's, catted H, M80's, FRPP frs-500 mufflers. So far, so good. The original setup was oem exhaust manifold, oem cats, oem H, FRS-500 mufflers..sound was good, no drone. After the lt's and catted H went in... WAY too loud,,and bad drone at 1900 rpm. M80's welded in, just b4 the axle... problem solved, barely any drone, and a deeper note, and overall level is way down to something I like.
Resonator's in general, might last longer, if placed after the H / X vs b4. That's speculation on my part.