If it had Bose speakers then there is an amp and sub under rear parcel shelf in boot...
May also be worth looking at wishbones in my experience on a number of 156's the TRW wishbones are noticeably lighter then a lot of cheaper alternatives (can't say all alternatives as don't know) and although not a huge reduction in weight it would have advantage of also reducing unsprung weight.
While looking at aircon compressor what about aircon rad as well.
Just a thought and not sure how do-able it is, not weight reduction but handling, if you could have a sump altered so it's shorter and run a dry sump system is there maybe some way with altered engine mount bushes you could lower engine even by an inch? As even a small amount on an engine with weight so high and forward may help handling.
Headlamp adjuster motors?