Z3/E36 parts

Since the Z3 is based on the E36 platform, are most parts interchangable? It seems like there are more aftermarket posiblilties for 318's than 1.9L Z3s. Thanks in advance

Sort of. Drivetrain up to flex disc, pretty much. Front suspension, I believe so. Diveshaft and exhaust, no, though you can cut several inches from a performance exhaust. Rear suspension, no. It is more like the E30 than the E36. Some stuff under the hood may be Z3 only.

Suspension parts aside, the engines are the same, yes?

internally, yes. There may be some little nuances with brackets and such, and I recall there being some differences mentioned when I inquired about a DA supercharger, but that may have been airbox diffences.