I just did the front end of my GN, along with a PST stock rebuild. I had a friend sandblast the A-arms, spindles, and brake backing plate, it you know of someone to do that. I just cleaned it off with brake cleaner then, and applied the POR 15. I applied it over the rust on the front sway bar. It will not stick to smooth surfaces anyway, and I have read about people having trouble with the frame areas if they are not prepped right.
If I had to do it over, I would also add the black metal topcoat over the POR 15, which you need for parts exposed to sun (not really the front end). I found a lot of info on the board in a search when I did mine also. Tim