How difficult is it to convert to pre facelift wide body.
Fenders, rocker panels, rear bumper? The plastic covers under the fenders.
The suspension, trailing arm is different. I think I'd do those as well. Drive shafts.
There's maybe a couple other things I haven't thought of. Go to realoem.com and compare your car with say a 2.8 of the same year.
I think if I'd gone to the effort of fitting a V8 to a Z3 then doing the wide body conversion can't be more difficult.
Surely everything is available from junk yard?