“Base” is the trim between 1958 and First Edition (in USA market). Often colloquially referred to as LCLC or Premium trim (technically incorrectly). I believe the technical term for the trim is actually “Land Cruiser” which is amusingly confusing. Premium isn’t a trim level, it’s a features package that can be applied to a trim level. I believe only the base/Land Cruiser trim can have the optional Premium Package, confusing the matter a bit, but there are base trims without the PP.
Aside from my journey into the land of pedantry, I agree with your actual point on the exhaust.