Lots of possibles with this one.
The coil could have been melted if the Leo's rpm wire (which will connect to a coil) shorted to earth at some point, may be worth checking this wasn't the case, could have accidentally fixed such fault changing the coil pack.
Can't remember what fuses run what on a P38 but shorting a coil pack to earth could potentially blow a fuse that runs some aspect of the petrol system, probably unlikely because would expect a relevant fuse to run the ignition (so wouldn't run on LPG either).
Emulators as Gilbert said.
Only other things that spring immediately to mind for this are forgetting to plug in the MAF (or ducting) / If an emulator isn't used (and yellow wires are used to disconnect petrol injectors) an issue in the Leo might have first caused the coil to burn, might now be causing Leo's relay (that joins / breaks yellow wire connection) to be unable to join yellow wires.
There are all sorts of ways of disconnecting petrol injectors if emulators are not used, yellow wires can be used directly or control a relay / a relay could be controlled by the blue wire.
Check positive feed to petrol injectors, check negative pulse at petrol injectors.
On either Gems or Bosch the fuel pump relay is switched by the petrol ECU which provides the relay coil's earth. I've known the petrol ECU to work perfectly except not provide the negative to the relay so the fuel pump never runs so obviously means it won't run on petrol (but will on LPG)... You've already ruled this out, I mention it because I was once called out to fix a P38 that would run on LPG but not petrol which (if memory serves) they said had recently had a failed coilpack. Wonder if a shorted coilpack could cause the ECU to fail in the way that sees it no longer provide the fuel pump relay coil earth. Discussed this with Gilbert before, he said he's known a P38 ECU to fail in the same way too but I don't know if that was after a failed coilpack.