Apologies for the super delayed reply, but thanks for your efforts Robert. My guess is as you described, these are probably proprietary. Another [Honda] Keihin ecu I replaced with an adapter harness had a Sumitomo connector on it which I was able to source somewhat easily, that gives me hope for this one!
Worst case I’ll just have to cut these off, or maybe 3D print a mating connector if I can find compatible terminals.