[andy]

Realoem shows the e36 323 going from '97 to '00. The pictures look to me like an iron-block M52, same as other 3 series.

The '97 & '98 Z3 were the only M52s (that I know of) that had an aluminium block in the US, previous to the e46 coming out.

If you want a light single-vanos OBD1 engine (just guessing here), then you need the head from an M50, and the block from a '97-'98 Z3. Crank can be from either engine, depending on what displacement you want.

The aluminium block is closer to 50 lbs lighter than the iron one, but a big pain to deal with. For example, the head bolts are special longer ones to get a better hold on the aluminium, and still commonly strip out even torquing them to factory specs.