like Spaz said, spacers with longer bolts are in order to bring the +42ET wheel out enough to clear the calipers from the spokes. If done right with a hubcentric spaces, no real problems here (I don't recommend tracking your car with this setup though).
This is pic is my friend Filippo's '90 318ic with Team Dynamic Monza wheels (18"x 8") ET+23. They came with a +18mm offset, but he had them custom machined down 5mm for a (E30) proper +23mm. I believe Team Dynamics offers all their wheels in a +18mm offset (which will fit an E30 fine unless it's lowered extreme like Filippos).