DEC VAX SDI interface via BDA?

I was poking about for alternatives to the hefty KDB50-Q SDI controller set for MicroVAX to connect up my Emulex SD590 SDI hard drives and found on ebay this item: http://www.ebay.com/itm/190665553055 DEC T1003 VAXstation BDA SDI 5015772-01 Disk Adapter to Single Drive Interface It is labelled as a VAXstation BDA (VAX BI Disk Adapter) and interestingly the T1003 is one component of the KDB50-Q board-set, so I am guessing this could be a VAXstation specific KDB50 all-in-one? anyone know anything about these? I could not find any manuals for them nor could I find a VAXstation that has some type of extensible bus that would support a board like this. I notice this seller has several other "VAXstation" boards too. I have a couple of M38 VAXstations but I don't think they take any type of expansion option other than graphics cards, so I guess the VAXstation BDA options go in the 4000 series? Looking at the few pages on the 4000 series does not reveal much in the way of expansion options either. thanks, nigel.