Others haven't but my rad got re-cored (higher fin count etc) but one of the other things they did was convert the rad to a triple pass. Thier thought was the water was passing through the rad too quickly, you may be able to do the same by slowing that pump down and avoiding the temptation to...
I and many others have used mini radiators on our micra engined mini conversions so it should cool adequately, you may want to add a fan though, mine was a Spal fan, a bit more expensive but fits beautifully.
You can see it here...
Happy to be corrected but afaik UEL headers are only really about sound, performance wise you'd ideally have equal length tubes to promote scavenging and generally 4-1 and short for top end hp and 4-2-1 and longer for low end torque.
I've pretty simply and easily converted my mini conversion back to a hydraulic clutch using the qg engine clutch pivot, I haven't tested it but from looking at it I'd be surprised if the clutch master from the qg engined car didn't bolt up to the firewall. It might give you the clutch weight...
Try talking to these guys:
http://www.cvt.co.nz/
As you might guess they're in New Zealand so relatively close to Australia, but seem the best source of help with these CVTs, still repairs don't seem cheap...
I think I remember someone saying the rear hinges on the 5 doors are the same as the fronts but because they are used far less don't get as worn, a cheap alternative could be to find some rear hinges at a wreckers and fit those.
I realise you're probably in the UK and it may not be the most useful but it may help.
https://www.cvt.co.nz/
https://cvt-parts.co.nz/overhaul-kit-electromagnetic-clutch/
Yeah, probably see how long it'd take to get a replacement first, trouble is going to be marking 5 degree offsets accurately and if it's moved once it's likely to move again.
They have a rubber sleeve that forms the harmonic balancer, I've heard they can move and effect timing that seems like what's happened here. Your best bet would be to get a replacement harmonic balancer either new or a replacement 2nd hand item.
They are both the GA block so I'd say physically fitting the engine will be the same as the ga16 the wiring for the ga15de is very similar so I think this could possibly use the k11 wiring loom but you'd need to check.
Engine mount at the timing chain end and clearance on the chassis leg are...
It did on mine, btw car still runs if the connection is broken(if your tacho breaks the car would still run), somehow... but gives an error code, seems the ecu monitors the return from the coil. You can intercept the wire closer to the ecu of it's easier for your wiring.
A leak down test to see if the cooling system holds pressure would be a good diagnostic, the water pump seals can leak so look for coolant coming from the small holes on the water pump. There's an O ring on the hard water pipe that goes into the back of the water pump housing that can leak...