For those who saw this item: https://www.ebay.com/itm/183639487495
but didn't know what it went to (Web searches for "5409818" and "5009817" didn't turn up anything useful for me), it turns out to be a "Configuration 2" backplane for a PDP-11/05-/10: http://gunkies.org/wiki/PDP-11/05#Backplane_versions with slots for one MM11-L memory unit, and 4 SPC slots. Noel
