Meh. Don't just wang the first nut up super tight and you'll probably be ok. Tighten opposites in turn nice and slowly and the taper on the nuts will centralise them. If you get a bit of vibration turn the wheel 90 degrees on the studs and have another go.
My old old slots never had any centre location, just careful tightening and were always fine, likewise the 7"s that were on the front of the red one. My current slip on spacers are the same. The only time I've felt compelled to use centre location is when I had no location on the studs using separate tapered washers and nuts to shuffle the 4x4" PCD of the wheels to the 4x100 of the studs.
