I hope you understand French because it seems that you can find what you want at this adress :
http://www.lpmi.u-nancy.fr/nubus/nubus.html
There are some schemas too at the end. They describe how to make a NUBUS analog interface card for Macintosh.
They say that Nubus is a standard from the M.I.T (www.mit.edu) and dell to Texas Instruments (have a look at www.ti.com and search 'nubus'... it gives 5 results, seems to be relevant), so it isn't Apple proprietary...
Hope this can help even if I spelled wrong too ;-)
