The original wheels for a '67 GS400 with disc brakes was a 14x6 rally wheel that is the same wheel that Chevy used in 1967. The code beside the valve stem is DG. Chevy guys say that Buick used Chevy wheels, but I prefer to say that Chevy used Buick wheels because the both started using them at the same time, 1967. Chevrolet used polished trim rings and center caps, while Buick used similar items but with the brushed finish. Buick also used these wheels in 1968 because the 4-piston calipers were still being used. There has been some debate about the color of the wheels when used on a Buick. However, they were definitely body color with certain colors. My car is code F (Blue Mist) and the wheels were painted body color. Red cars had red wheels (I've attached a picture from an original road test as an example). White cars however did not have white wheels (they appear to be black on the white GS400 in the April '67 Motor Trend road test article). There are some '67 experts that will argue that the wheels were always silver (argent) 100% of the time, just like a Chevy, but that is just not a correct statement.
I think you can get Rallye wheels from a number of suppliers. Back spacing is going to depend on wheel width, and year of vehicle. The 60's Buicks need more back spacing than the 70-72 Skylark/GS http://www.stocktonwheel.com/smoothie.html http://www.wheelvintiques.com/ http://www.specialtywheel.com/ You can find them in the Jegs and Sumitt catalogs too.
You'll have to wait for someone with an original 67 GS400 to come across this thread I guess. Not sure they make 14's. I think the repros are 15's.
I'm fairly certain that no one reproduces the correct center caps for the '67/'68 disc brake wheels but they pop up for sale on this board occasionally. Here is a set that appear to still be for sale and for a very good price. You can likely get the replacement trishields if you want to make make them look even better. http://www.v8buick.com/showthread.php?247449-1967-68-Disk-Brake-Wheel-caps&highlight=caps
chev and buick used the same rallye wheel for '67 and '68. probably true for olds and pontiac a-body cars. camaro would be the same, also. they were all 14" rims and unique only to both years - 4 piston calipers. the only 15" rims, at that time would be from the corvette but i not sure 15" rims were available.
