The last images you posted in this thread show the one drawback of D-76. Did you notice that there was an area of the image of the back of the station wagon that was oddly blurred? Sure, the blurred area was rectangular and about the same dimensions of the obscured license plate. I'm certain though, that the blurring was an artifact of development. D-76 is not nearly exotic enough for me. That very lack of exoticness is also the reason why the developer selectively scrambles the grain on your negative.
If I were you, I'd go to Photographers Formulary and order the most expensive dry chemical that develops film, spend a couple of months perfecting a formula that actually works, write an article about it that includes hundreds of pages of test data, defend your new formula against all scoffers... and then drop it favor of
D-76. D-76 is a great developer that has been around for 30+ years for a good reason. It works well with Kodak film.