That is an impressive Scotch mount.
I think that the Scotch mount (aka barn-door mount) was first described by G.Y. Haig in JBAA Vol 85, No 5. I’d only just joined the BAA in 1975 and this was the first paper that I found really interesting. I built a basic copy and used it for many years to take night-sky photos using a manually driven screw and a stop watch (things were hard back then). In the 1980s I built an advanced one which had a crystal controlled stepper motor drive and took this to Tenerife to photograph C/1996 B2 (Hyakutake).