I'll confess to cutting the door cards in mine shortly after buying it new in '76. I had ordered it with a Blaupunkt Frankfurt AM/FM radio and as I recall there weren't a lot of good options for where to mount decent speakers. As Karl points out, they were considered just average production cars and most of us were doing things like that.
Karl, it sounds like you're pretty familiar with this car. Do you know any more specifics about the engine build? Hi-comp pistons, which cam, etc?
Being a pre-1976, this car is smog exempt in CA. Looks very tastefully done.