The controller board has a 35-pin Ampseal connector, easily found on eBay and elsewhere. I’ve ordered one for now though I may end up ordering a second so I can do a tidier job on the final wiring.
UPDATE [2020-06-16]: It turns out AMPSEAL connectors are an absolute pig to crimp without a specialist £350 tool. I managed in the end but only on my second connector. The first one is probably salveageable but my advice is go slow and patiently, and don’t try to crimp in wire that’s too thin like I did. 0.75mm2 looks to be ideal.