I could see the 14's being an issue. Did you re-check w/the 15's & they required the .250" spacer?The previous rims I do not recall the offsets but they were 14x7s (I had to use one inch spacers up front) and 15x8s in the back is what the current owner used I just changed the mags last year. Right now I am currently using 15x7s up front and 15x8s in the back. If I remember rightly the front wheels I added a quarter inch wheel spacer and longer studs to give me some clearance and the back wheels I use the one inch spacer and took a little bit off the studs to make the rims fit because I couldn't get the offset I wanted. I'm not too sure about wheel spacers on the drive tires but I'm not cranking serious horsepower out of it so I'm not too worried the attached pics are the wheels I ordered from jigs I did swap out my center caps with the old mags.
I guess the SPC arms are usually intended for an app that would most likely have had larger diameter 'performance' wheels which likely would have cleared.