Z hood is for sure longer but I don’t think it’s heavier. I know the M (and I think all Z4’s?) have an aluminum hood, not sure about the e90/2.
If an online parts catalog is correct...
Z4M hood — 24 lbs
http://bmwfans.info/parts-catalog/41008041378
E92 hood — 38 lbs
http://bmwfans.info/parts-catalog/41617168514
I’d probably roll the dice with non-OEM, not a complicated part imo