cheers Anthony, it does feel long! I measured the stem ctc to be 120mm so you reckon find something around 100mm? I thought the stem was OE, the finish is lovely so i'll have to be picky if i do replace it!
Sorry, that must be the original stem then and I was fooled by the scale of the picture (doesn't take much).
I agree they're nice stems, but they're actually very similar to lots of other stems that were around on the market back then. Also similar to the contemporary Ritchey stems that you can often see for sale on eBay.
The geometry chart below shows how they used stem length as a major part of differentiating between sizes - in theory, you shouldn't because stem length should be all about steering characteristics, but it's evident that they used stem length and also seat tube angle to minimise wheelbase differentials. I think they're saying it's the lesser of two evils - i.e., a long stem deadens the handling, but a long wheelbase deadens it even more, so we'll go for longer stems and slack seat tube angles in the bigger sizes as well as longer top tubes.
The intended height range was roughly 5-0 to 5-6 for size 16, 5-3 to 5-9 for 17 and 5-6 to 6-0 for 18. So I guess you can look at the standard stem for each size and adjust according to your height. But it's only a reference point - in the end, it's all down to personal taste anyway.