No. Z31s dont fit.
Just get z32 rear from N/A and redrill front hubs to 5x114. Cheapest way to go 5lug.
lol i redrill my front set! worked great. i sold them and bought oem ones on ebay for $160 shipped BRAND NEW!!
oh...SEARCH>YOU
your sig pwns
type 240/40r18 into Google...
I'm disappointed when i see threads like this, that's all I'm saying, if you've done some searching then explain that and somebody can help you to find better places to look too.
-end mini rant.