I like the idea of blue with the black, very nice and a bit different.
Did you see the thread by Toot's on the NSRA forum about flames & scallops on kustoms? I love the second from last photo, not sure it would suit yours mind you.
agree with jd, ghost flames would look best, you have lovley paint on that beast and dont want to cover it up much. pale blue ghost flames. just my opinion