Yes, it sounds a little like a Xerox Daybreak, I think. I found one at a radio rally earlier this year for the very low price of \pounds 10.00, so it's now sitting alongside me. There are 5 slots in the Daybreak, although 1 or 2 may be empty. From the left, looking from the rear, you find 1 - Display control and memory 2 - Memory expansion 3 - Mesa Processor board (Bit slice processor using 2901's) 4 - I/O, boot procesor (80186) 5 - Option I/O. I've got a laser printer card in mine. If it's any help I've pulled the processor from slot 3 of mine, and it's a 140K05571. I can pull the other boards if you like and check the part numbers

Mine has a 5.25" drive in separate case on top. No reason why a 3.5" drive couldn't be used instead, of course (although this may not be an 'official' modificiation.