The S&R catalogue prescribes a 1500 balance shaft for a >1700 engine, so should be OK. I'm still not sure what the differences are: http://www.saab-v4.co.uk/speedball/topic.asp?topic_id=33271 I have 1700 balance shafts for sale if you insist on using one, but to be honest I wouldn't bother if you have a good 1500 balance shaft.
The Competitions Dept recommended the 1500 balance shaft to be used in 1500 and 1700 rally variants. See the Tuning Guide. I used to have a tuned 1730 motor and it too had the 1500 balance shaft. Just to confirm what has already been suggested.