It'll probably work fine without a reinstall. I can't guarantee it. But I doubt there will be much if any issues. I've done bigger generational leaps without a reinstall. The only time I've had an issue was going from an ancient G31 chipset to an H170 in Windows 7.
The biggest would possibly be Windows activation. If it does give an issue calling the MS activation line should clear it up as you are repairing a computer and all the other components are the same.
I managed to find a guy on Gumtree who was selling the same motherboard as my original, it worked almost straight out of the box. thanks for taking the time to offer some advice. My Son is back to just resenting me now! result