The 68-69 GS400 never came with 15" rims. They had 14 X 6" rims with 4 3/8" back spacing. You can use the 70 and up 15 X 7" rims, but the 68-69 really wants another 1/2" of back spacing to fit the biggest tires.
Comedians.....I have a set of 15" chrome wheels. I also have a set of 245/60-15 BFG Radisl TA's if you need tires too
Not Tony. I found Gerard over on BuickForums, https://buickforums.com/forums/threads/69-gs-400-emblem-hood-location.64508/ Not sure where he lives.