Whilst looking up information on the LGP-21 machine, one reference was to the journal “Computers and Automation”.
We might be able to name half a dozen manufacturers from the early 1960’s, but I was amazed that the pages of C&A are packed full of contemporary manufacturers offering every conceivable machine and peripheral device.
Their Annual Pictorial Report begins on page 26 - some intriguing festive reading:
The DSI 1000 on page 27 is particularly interesting. A 12-bit, 2048 word machine with a 3.2uS memory cycle time. Notably is its very compact size a 19" x 10" x 19" rack. As a contemporary of the PDP-5, it is a fraction of the size. Sadly no other information found on it - yet.
EDIT - the company behind the DSI 1000 was bought by HP in 1964 from Union Carbide - when HP first got interested in computers for instrument control.
The 12-bit DSI1000 was extensively redesigned by the original design team from DSI - now working as HP employees within their subsidiary Dymec company, and appeared commercially as the HP 2116A in 1966 - the first viable 16-bit minicomputer, preceding both the PDP-11 and the DG Nova.
The HP 21xx series of 16-bit machines would dominate the industry for the next 25 years.