I had a Nascom 2. I salvaged it from cruft in the workshop of that computer shop. It had the add on 32k DRAM board that was given free when there was a shortage of SRAM chips for the 8k of on board RAM. The DRAM board had Nascom memory plague and I had to add extra power bus-bars as the tracks on the PCB were too thin and a lot of extra .1uf and .01uF decoupling capacitors. It wouldn't run at 4MHz 0 wait-states but was OK with 1 wait-state.
I had a board we made up in the workshop that was used to slow down Nascoms to see if they would work but were being clocked too fast, i.e. check for marginal timing etc. It consisted of a 10 turn pot on a 555 and that drove the BUSREQ pin on the Z80, maybe there was a bit more logic that ensured all the other *REQ pins were sequenced OK. The result was you could turned down the effective clock rate of the Z80 but keep the DRAM refresh rates correct. ISTR you could slow it down by a factor of 500 which was great for finding faults. Or cheating at Space Invaders.
It was binned when I moved to GM 15 years back. Typing about 32k RAM makes me smile... I have a new PC for work, an Ultrabook. Quad core i7 gen5, 8G RAM 256G SSD. No optical driver, 13in 1920x1080 LCD, 802.11ac Wifi all in a cute package weighing about 1.5kg. Fantastic what has happened in the 36 years since that Nascom was on sale.