Hemmings '63-'66 Article Contains Some Dumb Errors
I would term them more half-errors. There was an aluminum slant block but I never understood it was an ordering option. It is said that Chrysler dropped it due to cost, though did have corrosion issues.
True that the V-8 had a single exhaust like the slant, but not same PN's, and it wasn't restrictive. Indeed, I have read that Chrysler tested a dual exhaust and found the single gave more power.