Click the link to download their entire speed sensor section of the catalog in PDF. My D300 is an '80 short rear output and uses the threaded speedo drive. They've got an adapter that screws into place with a sensor in it. It's also got a pass-through type fitting on the back so you can still use a mechanical speedo cable if you've got one.
I think they've got sensors for the long output D300 as well. They seem to be a pretty standard size. You'll probably need to call to figure it out for sure though.
