.5mm slop on each side really shouldn't be a problem with such a large hex.

I'm just glad to hear someone else is doing it before I take the plunge!
Here's some aluminum tape if you can't find any anywhere else:
http://www.davesmotors.com/s.nl?c=88...0mm%20x%202.5M
My suggestion for the tape would be to drive through a new residential construction area and ask any HVAC (heating ventilation air conditioning) guy for a little, they'll probably give you a roll! (that's how I put racing stripes on my '84 crx- uber cool!)