I always thought 67 ,68 grilles looked better too, but I still bought a 69....but I doubt I would put a 68 grille on a 69 even if it would work, and I do not know if it does .... Now, its your car and I always tell people to do what they want ,its their car,just enjoy it, but....in this case , I think you are making it very hard to sell later....I know, I know , you keeping it forever , but realisticly , everyone always sells at some time, or might come in a situation when they have to... I would think you are better off to "live with" a 69 as it is or a 67 or 68 as it is... We have seen some of those "Camobirds" (camaro front on Bird rears or vice versa) but it seems they get very hard to sell....
I know this is not an answer to your question ,but I think you might want to hear this too... Bjorn 69 vert.