I have ZX Spectrum Next board, and a fully cased one. I got a second pi0 to go into the cased one, so soldered the connector onto that - but then also trimmed the PCB standoffs that it needs as one of them is a bit too close to the audio jack.
Whilst it fits fine there, the standoffs are actually 1mm too high. The 40 pin connector makes contact but isn't fully engaged. In the cased Next, the ports won't line up properly with the back panel - so I'm going to either get some M2.5 11mm standoffs (correct size!), file down the 12mm ones a bit, or use the 10mm ones and some 1mm washers.
It's trickier than I expected finding M2.5 11mm in nylon - but I think just filing 1mm off the 12mm standoffs is fine.