Hi Ken,
I am guesstimating a length of around 67" and a wing area of around 800"square. These are pretty much the exact dimensions of the MK Skystar 90 (sadly, no longer kitted). I agree that 8.5 lbs is about the max. My Skystar weighed 8 lbs (or a little less) covered entirely in monokote and flew very well on 15% nitro. I think the Black Magic fuselage may be a bit larger fuselage (so, more drag); keep it as light as possible. Contest balsa, lightening holes where possible and minimal adhesive when sheeting the horizontal surfaces.
Good luck and keep us posted!
-Will
Of course you can always upgrade to a YS 115...