Joe, 880901(4) is the part number of the bellhousing, not the gearbox ID. The latter is stamped into the top of the "collar" on the bellhousing that bolts onto the engine. I think the easiest way to find out what box you have is to remove the bellhousing and check the diff. You could check the parts book and the Saab Sport and Rally Catalogue on my website, but I doubt they tell you much.
Melle - a while back I had a section in my 96 thread where I worked through several gearboxes to find the best one to use as a replacement. I wondered at the time if we could identify the manufacture date of the gearbox from the ID number. I assume they are sequential. Any ideas? I would like to try to figure out which of my collection of gearboxes was the original from the 96. Cheers and I hope this might help Joe too!
Gareth, I'm afraid I'm not very knowledgeable when it comes to gearboxes or how to ID them... Gearbox spec can be found in the factory workshop manual and the Sonett III supplement, perhaps the parts book may shed a light on MY changes. As far as I know, later boxes have a few bearings that are different to the early ones and the pinion and crown wheel are different for the Sonett (95/96 8:39 teeth, Sonett 9:42). I doubt there are details on race/ rally boxes in any of the books, maybe there's some info in the S&R Catalogue (http://www.saabv4.com/index.php/saab-factory-manuals/saab-sport--rally-catalogue/).