Thanks, and yeah it seems it was a fairly large revision, so even if it did work it might not be a great idea. What I didn't realise might be a potential issue is the compatibility with using an efan, which I plan to use. The '91 B230FT had a clutch fan I don't plan on using so it makes sense that earlier LH2.4 ECUs perhaps weren't set up for triggering a fan relay.
I guess that makes it all the more important to get this ECU or source another 9xx ECU for it, if this one is no good. Any idea if it's possible to identify whether that chip is the original for that ECU?
Additionally, I needed to test out the in-tank fuel pump, and the only way I could get it to prime/turn on was to hotwire the relay and the fuse to 12v. Does it require a crank trigger pulse to signal fuel pumps to switch on? I've had to require half my dash so trying to confirm I've wired things correctly.