What I'm missing is information (aka motherboard manual or service manual, NCR 3415 and other makers used these) so I can locate memory expansion boards for this motherboard: Been googling and ebay with no luck.
Motherboard: INTEL 637919-006 SYSTEM BOARD EBXX15MOR2

This is Intel made PCI and EISA motherboard has ability to take:
One Pentium CPU board, or two cards of single pentium boards (socket 5 type);

Also can take:
Single dual pentium processors board or Dual boards of dual pentium processors (4x pentium cpu total on two boards).

And also One or two Memory expansion board(s), this is required minimum of one memory riser to run since that motherboard does not have memory slots.

Thanks and cheers,