It wasn’t really a mod, but when the muffler needed to be replaced on my Datsun 180B SSS, the mechanic asked if I wanted a stainless steel muffler instead of the standard one. He told me that they last forever, never need to replace it again, so I agreed.
It was more cylindrical in shape compared to the standard, flatter muffler and scraped on speed humps, driveways and ruts on gravel roads. The baffle fell apart in it after about 9 months and it rattled noisily all the time. I had the irreplaceable stainless steel muffler replaced with a standard one about 18 months later.
