Well, time for an update on this.
I decided that doing an engine rebuild (properly) would be quite expensive so have been hanging around waiting for another option.
Eventually, one turned up, in the form of a 2006 DE saloon that had failed the MOT on rear suspension mounting points. Mechanically good though, even if partially stripped.
I picked it up and after fixing a fuel tank leak

I put a DI cartridge on, swapped the fuel rail as the FPR was missing along with the plastic insert and then programmed an unpaired ECU, carefully removing the immobilisor

She fired up, seemed to run OK, so this weekend I'm aiming to do an engine transplant